Welcome, all. Let's get started with today's webinar, titled Uterine Mesenchymal Neoplasms, New and Involving Entities, and Headaches. My name is Elian Suarez. I am a gynecologic pathologist and the Director of Surgical Pathology at The Ohio State University in Columbus, Ohio. I'm honored to be the Chair of the Pathology Education Group of IGCS. We thank you all for joining us today. For today's webinar, I'm really excited to introduce Dr. Brooke Howitt, who is an Associate Professor of Pathology at Stanford University School of Medicine, a very, very prolific author and opinion leader in gynecological pathology with interest also in the sarcoma world, in mesenchymal neoplasms. Dr. Howitt also has very relevant experience with global health, having practiced surgical pathology for a period of time in Malawi, and also teaching pathology residents in Rwanda. She also is a telepathology consultant for Rwanda and for Haiti. In today's webinar, Dr. Howitt will review new and evolving uterine mesenchymal entities, as well as biomarker and molecular assays to aid in this diagnosis. Additionally, appropriate diagnostic terminology will be covered in the absence of immunohistochemistry and molecular tools. Thank you for joining us today, Dr. Howitt. Before we start, I should mention a couple of housekeeping items. Please know that a recording of this webinar will be available on IGCS Education 360 Learning Portal within one business day. We encourage you that during the webinar, we encourage you to submit questions via the Q&A feature at the bottom of your screen. We will do our best to address as many questions as possible. Dr. Howitt, I will now hand the webinar over to you. Please share your screen. All right, is this looking okay to everyone? Looks great. Okay, great. Hi, everyone. Thanks so much for having me. It's a real honor to be able to present this talk today on uterine mesenchymal neoplasms, focusing on the newer and more evolving entities and the challenge in dealing with these in the absence of molecular assays in particular. So I thought today we would go over some updates in the classification of, as well as kind of review newer entities in our gyne sarcoma world. And this includes some new variants of high-grade endometrial stromal sarcoma, as well as better understanding and expansion of our understanding of uterosc, as well as covering the intract sarcoma and SMARC deficient uterine sarcoma. So the evolution of the practice of gynecologic surgical pathology, I think is really interesting and it mirrors many areas in surgical pathology, although we all tend to be progressing at different rates and everything still has its basis on H&E examination under the microscope, which I think is really fascinating considering the number and breadth of molecular assays that are now available. Of course, we may use a number of immunohistochemical stains to help us characterize, but again, it's always based on the morphologic assessment of what we're seeing under the microscope. And in some cases we may decide to do some sort of cytogenetic study, such as conventional karyotype or FISH. Of course, for FISH, you have to know exactly what your question is and what you're looking for. And I think nowadays in many regions, it's becoming more common to do bulk sequencing for both DNA and RNA to help us classify these lesions. And in some fields, particularly the central nervous system tumors, people are really working with profiling at the epigenetic level to help with classification of tumors. And there's some limited evidence in gynecologic mesenchymal tumors that this is also helpful, but it's probably not considered mainstream at this point in time. And so it's like every week, I would say, there seems like there's a new mesenchymal tumor that we need to learn about or a new molecular finding for an existing entity. And so the world of uterine sarcomas and mesenchymal tumors is really growing exponentially. And of course, we have our kind of fundamental foundational classifications of stromal and smooth muscle, which of course is challenging in and of themselves. But in addition, we have entities such as adenosarcoma, inflammatory myofibroblastic tumor, uterine tumor resembling ovarian sex cord tumor, intract sarcomas, peckomas. There's now a new sarcoma, which we aren't really sure exactly where it falls, but maybe in the stromal, maybe its own thing, the CANCEL1 or CAT6AB rearranged sarcomas. And then of course, we have our SMARC deficient uterine sarcomas, whether or not it's truly even a sarcoma is a little bit also in question, but that's what we're with right now. And then of course, the category that we refer to as undifferentiated uterine sarcoma as kind of an effect of all of these new classifications is actually getting smaller. So it's becoming much harder to call something an undifferentiated uterine sarcoma, particularly in the setting of availability of molecular assays. So low-grade endometrial stromal sarcoma, of course, there's nothing really particularly new here, especially when you have this very classic appearance, both by gross examination with this worm-like infiltration into the myometrium and extensive lymphovascular space involvement, which correlates very nicely with the HNE shown on the right. And in high-power magnification, these are fairly bland to kind of mildly atypical cells. Again, very ovoid-shaped nuclei in contrast to smooth muscle tumors, and they tend to kind of whirl around these small arteriole-like vessels similar to a normal endometrial stromal appearance. Now, where low-grade endometrial stromal sarcoma becomes a little bit challenging is when there is altered differentiation or variant morphologies, such as smooth muscle differentiation, sex core differentiation, and then there's a variety of kind of fibromyxoid to heavily myxoid to collagenous backgrounds that can make it difficult to recognize tumors as a low-grade endometrial stromal sarcoma. And then, of course, when you have glands associated with the tumor, it becomes challenging to distinguish in some cases as well. And unihistochemistry for low-grade endometrial stromal sarcoma, the classic panel that we think of includes CD10, ER, and PR, which if you have unihistochemistry, these are fairly accessible stains that most people have. There are some other stains that people use, but I would say most people don't have access to them, so I'm not covering them here today. And then a stain that is helpful for negativity in low-grade ESS is cyclin D1. And then, of course, our smooth muscle markers, which are a little bit tricky because in the setting of smooth muscle differentiation, the smooth muscle markers, of course, can be positive. So, this is an example of a low-grade ESS that has pretty significant desmin positivity and kind of negative or maybe just very focal limited caldesmin positivity. Ancillary tests that we can use to help support the diagnosis, particularly in the setting of unusual morphology or unusual aminophenotypic features include cytogenetic approaches such as FISH or a targeted RNA-seq panel. Of course, the goal here is to identify a fusion or rearrangement typically at the JASF1 or PHF1 locus. And there are some examples that lack demonstrable genetic rearrangements, but I would say the proportion of cases in this category is getting smaller and smaller as we're learning more about other forms of uterine mesenchymal neoplasms. So some of the pitfalls that I think are really important in diagnosing low-grade ESS, and these things are particularly important in the setting of labs or folks who are practicing who don't have access to molecular testing, is just to keep in mind that cellular smooth muscle tumors can have a lot of morphologic overlap, at least at low power view, and they can also be CD10 positive. So here's an example of a fairly cellular blue-from-low-power tumor that has a little bit of irregularity in its interaction with the surrounding myometrium, which we're taking a little bit of a closer look here. And you can see, additionally, this clefting is very prominent in big, thick-walled vessels at the periphery, and it's centrally as well, but probably most prominently in the periphery of the tumor. At higher magnification, you can see that the nuclei are somewhat oblong, but maybe not your typical smooth muscle-type cigar-shaped nuclei, and they are not growing in fascicles formed by these spindled cells with abundant cytoplasm, so you might be wondering if this is actually a stromal neoplasm, and if you were to put CD10 on this tumor, you would see that it actually was quite positive, and it also is positive for all of the smooth muscle markers, and this is a really common question that I get asked as people get thrown off by the cytomorphology plus the CD10, and could this be a low-grade ESS or a stromal tumor? And this is, in fact, a cellular leiomyoma, and I think there's a lot of things that we can learn from this type of case, and the first is that CD10 positivity does not mean it is a stromal neoplasm. This theme will pop up again when we talk about newer and additional entities, and a careful morphologic assessment in the distinction of a cellular smooth muscle tumor from a low-grade ESS, I think, is probably the very most important, and the IHC is oftentimes not that helpful. Of course, the molecular testing can be helpful, but it's really not required in most cases. So here's just a little table of the morphologic features that I look at when I'm trying to make a decision about a cellular smooth muscle tumor versus a stromal neoplasm, and the first thing that I look at are the vessels. In smooth muscle tumors, you really almost always see thick-walled tumors that are pretty abundant, and they're present throughout the tumor, and in stromal neoplasms, they tend to have this much thinner-walled vasculature, arteriole-like in nature. You can have some thicker vessels at the periphery, but certainly not throughout the entire tumor. On higher magnification, and of course, this becomes less helpful when you have a very highly cellular smooth muscle neoplasm, but I always look for elongated and kind of blunt-ended nuclei to support it being a smooth muscle tumor versus more like fusiform and ovoid cells for stromal neoplasms. Another thing that I look for in smooth muscle tumors is this very prominent clefting from the background myometrium, and you can also end up with this kind of plexiform-like pattern, and somewhat irregular borders are acceptable, and they're actually frequently encountered in the setting of cellular smooth muscle neoplasms. Immunophenotype, as I mentioned, is not always helpful. It can be helpful if you have really strong smooth muscle positivity and CD10 negativity, then it is helpful to support the diagnosis of a stromal neoplasm, but it's really important to remember that smooth muscle tumors can have a significant amount of CD10 positivity, and of course, if we were to go for molecular analysis, the finding of JASF1 or PHF1 rearrangement or fusion, of course, would support a stromal neoplasm. This is another example of a tumor that maybe on first glance has some similar appearances. It's very cellular, very blue, has some hints of fascicular growth, at least from this medium magnification. I will point out this border with the myometrium is highly unusual. It may, from first glance, appear to be well circumscribed, but if you look, it's actually infiltrating in a fairly destructive way these bundles of myometrium that it's coming into contact with, and here's just another closer-up view of this tumor that is kind of engulfing and enveloping smooth muscle bundles, which is very different than the finger-like delicate projections that we see in cellular smooth muscle tumors. Again, here's the cytomorphology. Spindled cells, not particularly blunt-ended, a little bit pointy-ended even, but kind of nondistinct morphology, a few lymphocytes scattered around, but I would say maybe moderate atypia, some mitoses, but not a lot of mitoses. Well, this woman ended up, this was called a cellular leiomyoma, and then this woman presented here at Stanford for workup of a lung mass, and this was a biopsy of the lung mass, and you can see it has some similar features, but in addition, it also has this really prominent myxoid stromal background, and this is the desmin, showing that it is strong and diffusely positive for desmin, and this is the ER, which is quite strong and diffuse, again, supporting origin from the uterine tumor, and when we go back and look at the uterine tumor, I should say this lung tumor was sent for fusion sequencing and was identified to be harboring an ALK fusion, and so we went back to the uterine tumor and got the block for that, and sure enough, ALK immunohistochemistry is positive in the uterine tumor, and so now I have expanded my morphologic spectrum of things that I think about for inflammatory myofibroblastic tumor of the uterus that can very closely mimic a cellular smooth muscle tumor, and really the main difference was the way it was interacting with the myometrium, and so now whenever I see that, I always consider the possibility of a non-smooth muscle tumor, so some practical pearls, I think in general, if you have access to ALK immunohistochemistry, I have a pretty low threshold for ordering that, especially with any amount of myxoid stroma, unusual morphology or infiltration of the surrounding myometrium, and one thing I always keep in mind is that while the molecular is consistent across the tumor, the immunophenotype or the degree of positivity for ALK actually often can correlate with the degree of myxoid stroma, so if I have a lot of blocks to choose from, I'm going to pick a block that has the most myxoid stroma to do my ALK immunohistochemistry, but of course, for molecular testing, you can select any block with good lesional tissue. This is a new entity where I think it causes many of us a bit of stress and confusion, mainly because there's no specific immunophenotypic profile, and very few, if any, have access to a molecular test to identify these tumors, and this is the CANCEL1 fusion tumors. It's a Cat6a or Cat6b fused to CANCEL1. These tumors have morphologic features that are really hybrid between smooth muscle tumors and stromal tumors. They can demonstrate both smooth muscle marker positivity, although it's usually more focal or limited, as well as CD10 positivity. Again, it tends to not be diffuse and strong, and unfortunately, the kind of the worst part about this is that not only are they hard to identify definitively, but they also can be associated with, oh, what just happened? Sorry, something popped up on my screen. They can also be associated with aggressive clinical behavior, despite an often bland histologic appearance, and in one of the initial reports of these, a series of these tumors, a quarter of patients were dead of disease at a median of 10 months, and some of these tumors were tumors that had a mitotic count of 1 per 10 high-powered field, which is quite low, so this is a little bit terrifying, and I don't have a great answer for how to identify these tumors yet, but I'm sure something will be cooking any time now. This is just another look at these tumors. Again, they can be very cellular, very blue from low power, well circumscribed in many cases, and they can have this kind of delicate infiltration, similar to what cellular smooth muscle tumors do, where they, rather than kind of destructively invade the myometrium, they kind of just protrude and extend into, but this pattern can be quite variable. Another interesting feature of these tumors that maybe can be a helpful morphologic clue is this abrupt transition from a more kind of hypocellular, somewhat myxoid appearance with pretty small arteriolar-like vessels and more of a whirling-type growth pattern, which abruptly transitions to a more spindled, fascicular, and more kind of compact growth, which is present in many cases, and then, of course, here you can see this kind of delicate branching vasculature, which also is variably present in these tumors. So this is one of the kind of new and evolving entities. Certainly it's a new headache, where it's unclear how common these tumors are at this point in time. There are some older reports of these tumors in the literature as just leiomyomas, and so it's kind of really unknown if these are going to be a subset of smooth muscle tumors or stromal tumors, or will they be their own entity? I don't think we really have the question, I mean the answer to that question yet, and I think the distinction from cellular smooth muscle tumors in particular can be really challenging, and there's no molecular assay to help us with this distinction. The one thing that can be helpful is if you have really strong diffuse positivity for all of the smooth muscle markers, you're probably not looking at one of these tumors. But again, this distinction is very important given the potential aggressive behavior of these tumors. Okay, so moving on to high-grade endometrial stromal sarcomas. Again, these are not necessarily super new, but they've kind of been described in the last five to seven years in more detail, at least the B-Core ones. And the definition, you know, we keep using the same words, low-grade ESS and high-grade ESS, but their meaning has changed over time. So before, you know, about 20 years ago, high-grade ESS and low-grade ESS were not defined the way that they are now, and it was largely based on mitotic index. And then for some time, we actually got rid of the term high-grade ESS, and there was just low-grade ESS and undefuterine sarcoma. And then in 2014, they incorporated high-grade ESS back in, which was very strictly defined as YWHAE rearranged sarcomas. And then with the discovery and description of B-Core sarcomas, B-Core was then added to the mix in this category of high-grade ESS. And so that's kind of where we are now. And there are a few tricky areas, I think, that we've kind of come to realize as we gain more experience and have more tumors that are molecularly profiled. So just to review, the YWHAE rearranged high-grade ESS, this is a tumor that can have permeative and infiltrative growth into the myometrium. And from low power, you can see that these tumors have this very distinctive vasculature. It's very thin-walled and delicate, but with a branching vasculature that can impart the appearance of a very nested growth to this very epithelioid tumor. These tumors are generally negative for CD10 and strongly positive for cyclin D1. And of course, the canonical molecular features of these tumors is the translocation between chromosome 10 and 17, resulting in a YWHAE net fusion, which can be detected using karyotype, FISH, or RNA-seq. So where does it get challenging? So the YFAM high-grade ESS are challenging because, in some cases, they can have associated low-grade morphology. So both of these are examples of a high-grade ESS harboring a YWHAE rearrangement, but with some component that demonstrates a low-grade morphology. And I want to point out that they tend to have a little more abundant cytoplasm, and they look a little bit more fibromyxoid in character compared to your totally textbook low-grade ESS. These tumors, in addition to having morphology suggestive of low-grade ESS, are also tend to be positive for CD10, although not 100% of the time. And additionally, you can even see areas that look a little bit more kind of blue and hypercellular, and then you have these little nests of cells that are much larger, more epithelioid, more cytoplasm, and very vesicular nuclei, more typical of high-grade ESS. And so you can either have a pure component that is low-grade adjacent to a high-grade, or you can have little nodules and nests of high-grade-type morphologic cells arising in a more low-grade type background. And I hate to tell you, but in some cases, YWHAE high-grade ESS, the tumor is composed entirely of low-grade morphology. And this can be quite tricky. The good news is that when they do this, they tend to have, although not always, this fibromyxoid morphology. And additionally, they can have CD10 negativity or only focal staining, as well as limited or focal hormone receptor positivity. And even in the setting of lower-grade morphology, they can still have cyclin D1 positivity. So any kind of funny morphologic feature, and definitely including any time I see fibromyxoid stroma, I always want to do the full immunohistochemical panel if I have that available, and in some cases, molecular testing as well. And I would like to point out that one of the recent reports said it was unclear if these tumors are best classified or diagnosed as a low-grade ESS or high-grade ESS for treatment purposes. I myself have seen one of these pretty recently in the past couple of years, purely low-grade ESS in the uterus and presented with high-grade morphology, distant mets, and has now recurred multiple times. So I am kind of of the mindset, let's keep it as a molecular distinction. And even if they have this fibromyxoid lower-grade morphology, if they are found to have a YWHAE rearrangement, I think it is better to put them into the high-grade ESS category. So the other flavor of high-grade ESS, of course, is the B-core altered uterine sarcomas. And here you can see these also can have kind of lobulated, permeative, and infiltrative growth into the myometrium. They're composed of spindled and round cells with variably, but almost always at least focally, myxoid stroma. And I think that this characteristic kind of bubbly, evacuated background in this myxoid stroma is also a common feature encountered in these tumors. They can also have a bit more of kind of a densely collagenized stroma, can be highly cellular, and demonstrate kind of moderate nuclear atypia. Immunophenotypically, these are often CD10 positive. They should be negative for all smooth muscle markers, and they are diffusely positive for cyclin D1, just like the YFAM high-grade ESS. And so this was an example of a B-core fusion uterine sarcoma. This is a tumor that can also be confirmed molecularly, either using FISH or RNA sequencing. And one of the unusual morphologic features of the B-core sarcomas, and I don't know how much it's really emphasized, is that fusion sarcomas in general have often been considered to be more of a uniform atypia, and they tend to lack overt pleomorphism, at least in a severe form. And I've seen now quite a few examples of B-core high-grade ESS with molecular confirmation that have pretty striking nuclear pleomorphism and variation in size and shape. So here's just one example here. Here you can see, again, quite a lot of nuclear atypia, and I would not classify this as being uniformly atypia, and they can be multinucleated here. And so just something to keep in mind, that if you see this degree of atypia in the uterus, it really does not exclude a fusion-associated uterine sarcoma. So whenever I see a sarcoma or something that looks like a sarcoma in the uterus that has both round cell and spindled morphology, especially with prominent myxoid stroma, I'm always thinking of a B-core sarcoma. And it's important, as I mentioned, to remember that these sarcomas can have a significant amount of nuclear atypia and pleomorphism, as well as the fact that CD10 can be quite strongly positive in these tumors. And although the smooth muscle markers are generally negative, they can have very focal desmin positivity. And then another thing to remember, in case you have access to, or you have heard of B-core immunohistochemistry, it's really important to remember that B-core sarcomas, about 50% of them are negative for B-core IHC. So the IHC is not a surrogate for fusion or molecular status in any way. So just keep that in mind. So this, then another example of B-core sarcoma is the internal tandem duplication sarcoma. The ancillary tests in this one, CD10 is variable, but usually negative. And again, cyclin D1 is always positive. So cyclin D1 is probably the most consistent, diffusely positive marker for all of the high grade endometrial stromal sarcomas. And the ITD tumors are a little bit tricky, even trickier than the fusion B-core sarcomas, because they will be actually negative for gene rearrangement, if you were to look at just a fish assay. And there are some sequencing assays like targeted RNA or DNA assays that can do, that can detect this internal tandem duplication, but it often requires an experienced and manual review. And so you'll have to check with your individual lab to find out if they can identify the B-core internal tandem duplication. So this is just a summary of the endometrial stromal sarcomas. Again, the morphologic features are pretty, pretty different with the exception of low grade areas within a high grade endometrial stromal sarcoma. And again, for the B-core sarcomas, you're really looking for that myxoid and vaculated background in the setting of both round and spindle cell tumor cells. Immunophenotypically, probably the most useful marker is cyclin D1, which is consistently negative or patchy in low grade ESS and strong and diffusely positive in all flavors of high grade ESS. As I mentioned, B-core is not useful for the diagnosis of high grade ESS associated with B-core fusion. Interestingly, when you look at the YWHAE high grade ESS, they are almost always positive for B-core. So it's really not a specific marker with respect to the flavor of high grade ESS. Hormonal markers can also be positive as they tend to be fairly positive, strongly positive in low grade, but negative or only focal in high grade tumors. And of course, we have a number of molecular assays to help us with this if you have it available. And it's really important, I think the main distinction is really between low grade and high grade. I think if you're not able to tell for sure if it's a YWHAE high grade ESS or a B-core high grade ESS, that may not be such a problem. But trying to make the distinction between low grade ESS and high grade ESS may be helpful. So some practical kind of tips in my approach to the workup of these stromal neoplasms. I generally do a panel of CD10, ERPR, and cyclin D1, especially in the setting of very kind of typical low grade ESS morphology. And if there's any kind of unusual morphologic features present, I would, you know, for example, smooth muscle type morphology, I would order the smooth muscle markers. If I saw something that looked like sex cord differentiation or really epithelioid morphology, I might order some sex cord markers. And again, just to reemphasize the point that the specific block or area of tissue that you look at for immunohistochemistry does matter, which is in contrast to molecular. And so when do I consider molecular? I think straightforward cases of low grade ESS with very typical morphology. And if you have a typical immunophenotype, there's no need to try and pursue any kind of molecular assay. However, in my practice, I do usually attempt some sort of molecular confirmation, whether by FISH or sequencing, in any case with unusual morphology or unusual immunophenotype. And I still make an attempt to try and subtype the high grade ESS by doing molecular confirmation. But again, I think for clinical management, this is probably not necessary. And another situation in which I will kind of go to try and do a little bit more characterization is in the setting of a high stage of recurrent disease, where these patients are likely going to be getting systemic therapy. And one thing to keep in mind is that before you diagnose an undifferentiated uterine sarcoma, particularly one that has uniform nuclear atypia, I like to do some sort of molecular, either a fusion assay or at least FISH to exclude both YWHAE and B-COR. Okay, other mimics of stromal tumors include, this is an example of a tumor that, sorry, is not the greatest picture, but this is a tumor that is highly infiltrative into the bundles of smooth muscle and also has some focal lymphovascular invasion. This is a tumor that is negative for both CD10 and cyclin D1, which is in contrast to the stromal neoplasms that we talked about. And so this is a uterine tumor resembling ovarian sex cord tumor or UTROSC, a potential mimic of endometrial stromal sarcoma in some cases. Now, when they have this morphology where it literally looks like a sex cord tumor in the uterus, it's generally not a challenging diagnosis to make. And this is a really interesting tumor that classically has a wide variety of morphologic appearances and also kind of varying architectural growth patterns. You usually have some areas of epithelioid type architecture and growth, as well as spindled components. This is a tumor that I think people have, you know, on and off proposed to be of endometrial stromal origin, although there's been very little immunophenotypic or molecular support for that theory. And as such, it's really kind of an unknown cell of origin type tumor. And immunophenotypically, these are kind of crazy tumors. They're polyphenotypic. They have marker positivity for epithelial. It can be smooth muscle, melanocytic sex cord. They can have a whole hodgepodge of positivity. And as such, if you're kind of struggling to make the diagnosis, you may have to order a pretty large panel of immunohistochemistry, immunohistochemical stains in order to help make that diagnosis. These tumors are interesting because they are, the malignant potential is still, I think, being worked out, but at the minimum, it's considered to be of uncertain malignant potential. And in one series, which is probably a little bit biased towards more aggressive behaving tumors, there was nearly a quarter recurrence rate and a significant number died of disease. And also this was reported before we knew about the genetics, which we will talk about, I think, in the next slide. So as I mentioned, immunohistochemically, these tumors will have variable positivity. There's no one marker that will be positive in all cases. But the sex cord markers like SF1, if you have FOXL2, Calretinin, and Hibin, those are all potentially positive in this tumor. Keratins are often positive, smooth muscle markers, HMV45, melanin A, all of these things can be positive and can be negative. The one marker that really should not be significantly positive in these tumors is CD10. Now, molecularly, we first thought these tumors to be associated with NCOA fusions or ESR, with usually partnered with ESR1, but there are now a whole host of other partners have been described. And this was present in about 75, 80% of cases. But over time, it was recognized that there was a different type of tumor that was associated with a GREB1 partner, either with NCOA genes or with a variety of other partner genes. And these tumors had quite different morphology compared to the classic kind of appearance and textbook description of uterosc. And these are, to me, look a little bit more just like sarcomas, like overt sarcomas. They tend to have more atypia. They have this kind of very compact growth pattern. And they lack a lot of the architectural variety that was seen in the originally described uterosc tumors. And there's also a lot of kind of evidence that these GREB1-associated tumors behave more aggressively than the tumors that are associated with ESR1-NCOA fusions. So what can we do to recognize these two different flavors of uterosc without molecular testing? Well, there's no perfect way to do it, but there are some trends. So the ESR1-rearranged uterosc are more likely to have the very stereotypical, overt sex core differentiation, both by morphologic assessment as well as by immunophenotype. These are more commonly postmenopausal women and in a submucosal location. And the GREB1-rearranged tumors tend to have a much more poorly developed sex cord morphology, less likely to have sex cord IHC positivity. And they tend to occur in younger women who are usually premenopausal, and they tend to be deeper in the wall of the uterus, so intramural location. So kind of all of these things taken together can help you make a guess or hypothesis about which one it is. Of course, if you wanna know for sure, you're gonna have to do the molecular testing. There's no immunophenotypic, or immunostain, I should say, to recognize either of these entities. Okay, and I think that we're getting close to the end here. This is another kind of newish sarcoma. Of course, it's also been described outside of the uterus, but now we know that these tumors do occur in the uterus, usually centered in the cervix, but can also involve the corpus. They are a spindle cell sarcoma. They can have this kind of adenosarcoma-like morphology. And one of the classic features is they have this very typical, highly infiltrative growth pattern. So they will just surround and diffuse through any preexisting structures, such as glands. And immunophenotypically, these tumors are positive for CD34, S100, and CD10. And if you have it, the Pantrac immunohistochemistry, but honestly, I actually think the combination of these three markers are the most helpful. And this is a tumor I think you can make a pretty good diagnosis of without molecular testing. So these tumors tend to either harbor NTRK1 or NTRK3 gene fusions. And there is this Pantrac IHC, it is not specific. It can be seen, positivity for this marker can be seen in many uterine sarcomas that do not harbor an NTRK fusion. And if you are able to confirm with a molecular assay, you should, or you can, and particularly in the setting of some kind of unusual immunophenotype. And here's just an example of, of course we have, this is an endometrial biopsy for retained IUD. And this is her proliferative endometrium here. And then we have this chunk of cervix where the stroma actually looks a little bit funny. It's a little bit hypercellular. It's got some atypia, kind of this whirling kind of story form like growth and scattered lymphocytes. This is the CD34, the S100, and the Pantrac. And this tumor was found to be an NTRK I fusion associated sarcoma. So prognostication in these tumors is really interesting. And I think it's still kind of a question mark. There's been one study of 15 cases, although not all cases had clinical follow-up available. So I would say that our data are still very limited with respect to precise prognostication in these tumors. But the features that you might be concerned about risk of recurrence are the usual suspects, necrosis, lymphobascular invasion, high mitotic count. And they did find that the presence of NTRK III fusion tends to behave more aggressively than NTRK I. And tumors that lacked all four of these features tended to not recur. But again, this is with the caveat of limited numbers that have been studied to date. And why is it important to recognize these tumors? Of course, because there is targeted therapy available. This is usually only in the setting of metastatic or recurrent disease, but it's just important to be aware of. And so adenosarcoma is a really interesting tumor, and I'm not gonna spend any time talking about it, but I think, or maybe I didn't mention for uterost, there's some morphologic overlap with adenosarcoma as well as a molecular overlap within COA fusions. And as I just showed you, the NTRK sarcoma can also have adenosarcoma-like features. And embryonal rhabdomyosarcoma has, for a long time, been known to have overlap with adenosarcoma, and the distinction can be quite challenging in certain situations. B-Core high-grade ESS can also have this kind of adenosarcoma-like phyloidiform architecture. And then SMARC-deficient uterine sarcoma, which is the one that I wanna talk about now, but it's really interesting because we used to call all of these things adenosarcomas, and over time, we're kind of peeling away little subsets of things that we used to call adenosarcoma, and we're calling them something else now. Okay, so SMARC-deficient uterine sarcoma. This is a relatively newly defined entity, and it is characterized by a bilelic loss of SMARC-A4 or BRG, as you might think of it for the immunohistochemistry. This is a tumor composed of highly atypical, but tends to be uniformly atypical epithelioid cells, which are somewhat similar in morphologic features to small cell hypercalcemic type of the ovary large cell variant. And that's actually how these tumors were first identified. And some of the interesting features about these tumors is that they can have an adenosarcoma-like morphology, and in fact, a third of cases have this phyloidiform-like architecture, and in some cases, it can be quite striking. However, I just want to point out from low power, in contrast to adenosarcoma, where the tumor is really defined by this very close relationship between a spindled sarcomatous component and the overlying benign epithelium, SMARC-deficient uterine sarcomas with phyloidiform architecture are rather just characterized by these clumps and nests of epithelioid cells just kind of blowing through the tissue without any particular relationship with the epithelium. And you'll also see a lot of lymphovascular invasion in these cases. So these have likely, kind of in years past, been reported as malignant rhabdoid tumor of the uterus. And as I mentioned, they're characterized by SMARC-A4 mutation with essentially no other genomic alterations. These are really kind of terrible, aggressive tumors that affect young patients, and almost all patients are dead within a year of diagnosis. They have very limited immunophenotypic or immunochemical positivity for any stain. They can have very rare keratin or EMA positivity, but extremely limited, and they're usually negative. Focal ER may have some focal CD10, just like every other tumor we've talked about today, and they can be WT1 positive. And another reason to identify these tumors in kind of in addition to its aggressive behavior is that they have been associated with germline mutation. So it is important to recognize similar to small cell hypercalcemic type of the ovary. And then even though this is a sarcoma lecture, and this is kind of, we've put it into this category of a SMARC-deficient uterine sarcoma that has a lot of overlap with adenosarcoma, at the other end of the spectrum, it can have a lot of morphologic overlap with an undifferentiated carcinoma, which should always be remembered in the differential for something where you are considering a uterine undifferentiated sarcoma. It's important to remember the possibility of a carcinoma because they can actually have a lot of morphologic overlap. And so this is one, the one on the left is the SMARC-deficient uterine sarcoma. The one on the right is an undifferentiated endometrial carcinoma. Now, molecularly, it can be much easier to distinguish these than it is by morphology and IHC. And you can see here, a SMARC-deficient uterine sarcomas have essentially no alterations aside from the SMARCA4 in contrast to undifferentiated endometrial carcinomas, which have a smattering of typical endometrial type mutations. Similarly, SMARC-deficient uterine sarcomas are genomically stable and tend to have very few copy number alterations in contrast to undifferentiated endometrial carcinomas, which tend to have some degree of aneuploidy in all molecular subgroups. And lastly, I mentioned methylation profiling or epigenetic profiling as a way to kind of help classify tumors. And if you look at these tumors in contrast to endometrial carcinomas, undifferentiated endometrial carcinomas and high-grade serous ovarian cancers, they really do tend to cluster quite closely with malignant rhabdoid tumors and quite distinctly as its own entity. And so some of the things that I think have been really fun over the past few years is just navigating all of these discoveries and new molecular findings. And are they variants of existing tumors or are they entirely new entities? B-Core high-grade ESS, I think when it first came out was a little controversial and people didn't want to call it high-grade ESS, but I think now we've kind of firmly landed in the, this is a variant of high-grade ESS. GREB1 uterost similarly had a similar debate of this. Is this a form of endometrial sarcoma or should this be under the umbrella of uterosc? I think right now, people are still largely putting it under the umbrella of uterosc, but I think that that is still an evolving concept. And then the NTRAC sarcoma, of course, pretty much immediately got its own, its classification as its own entity rather than being a subtype of another tumor such as adenosarcoma or inflammatory myofibroblastic tumor. Which brings me to another interesting point. Is inflammatory myofibroblastic tumor, how do we define a tumor when it looks like this with this beautiful myxoid stroma and inflammatory background, it's easy to call it an inflammatory myofibroblastic tumor. But in the literature, you can find quite a few examples of smooth muscle tumors, including leiomyosarcomas that are harboring, so-called harboring ALK fusions. And we have some examples of IMTs that have regions of the tumor that look indistinguishable from a leiomyoma. And so the question becomes, how do we define something like an IMT? Do we define it based purely on morphology or do we define it in a molecular fashion? And I think that there's a disagreement and controversy in the field here as well. And just, I am not gonna go through all of these, but, and it's probably, this is not a comprehensive list. I haven't checked this week for any new entities that have been reported, but there is a whole host of fusion sarcomas that are happening in the uterus and it's really hard to know how to classify them and what to do with them. And so I think that this is a rapidly evolving area in gynecologic pathology and it's going to be fun to see where that goes. Okay, so in summary, endometrial stromal neoplasms, of course, we have our low-grade and high-grade with the new entity or newish entity being the B-core high-grade ESS. The cancel one rearranged sarcomas are a real headache and we don't know where they fit and we also don't know how to accurately diagnose them at this point in time, but they are out there and it's important to think about. And if you see one that you think might be one of these tumors, I would say, find someone that you could send it to who can potentially do the test, even if it's just on a research basis, so we can learn more about it. And then there's a whole host of other mesenchymal neoplasms that harbor fusion transcripts, particularly uterus IMT and entract sarcomas that we talked about today. I didn't spend too much time talking about it, but there are a number of other gynecologic sarcomas that can also have fusion transcripts as like a path of driving pathogenic alteration, but it tends to be the minority of such examples. And really these tumors are, they require at least some IHC in many cases. And if you have the ability to send for molecular, it is helpful, but I think, we have to use whatever resources we have available. And I think with that, I can answer your questions. Thank you, Dr. Howard, that was really illuminating and at times terrifying to use your word. I'm almost certain I have a cancer one tumor that I can show you and share with you. So we have a number of questions. First one is, do you use ALK1 or D5F3 or know if there's any substantive difference between them when diagnosing urinary IMT? I think in the uterine tumors, it probably doesn't matter too much which clone you use. And we have seen, we get a lot of outside materials and so we see labs using different clones than the one that we use. And it, I have not seen any major variation based on that. Another question, are B-coarser lymphomas with a PPF P53 mutant? No, they do not. They do not tend to have, yeah. All right, which smooth muscle IHC marker do you consider sufficient to support the diagnosis of a smooth muscle tumor? Would you accept a desmig-negative tumor as being of a smooth muscle origin? Yeah, that's a great question. And there's, it's tricky because there's not really one. And I, you know, I often think of it as a hierarchical like SMA is the most sensitive and then desmin and then caldesmin. But I have seen increasing examples of desmin-negative, caldesmin-positive tumors. And so I have basically just started doing all three. And if I have two, two that are positive, then I usually accept it as a smooth muscle tumor. Can you still diagnose cellular leiomyoma if you have low power atypia, non-necrosis, non-mitosis? Well, it would be a leiomyoma with bizarre nuclei, I suppose would be the term. All right, and is it common for NTRK sarcomas in the cervix to infiltrate around normal glands without growing as a large mass? Yes, it can do that. So they can form like slightly exophytic or polyploid masses, but they don't have to. They can essentially be kind of almost imperceptible clinically and be growing into the wall of the cervix and infiltrating all of the glands without forming like a palpable mass, for instance. I can see that being very, very easy to miss on a CureTouch specimen. Yeah. All right, so I think those are the questions we have. Thank you so much, Dr. Howard. This was amazing. And again, this is the time we have for today. The recording of today's sessions will be available in one business day. Wish you all continued health and safety. Thank you very much. And until the next time.

webinar

Dr. Brooke Howitt

uterine mesenchymal neoplasms

low-grade endometrial stromal sarcomas

high-grade endometrial stromal sarcomas

B-Core sarcomas

NTRK sarcomas

immunohistochemistry

molecular testing