The "Other" Uterine Mesenchymal Neoplasms: Recent Developments and Emerging Entities.

Uterine mesenchymal neoplasms are a challenging group of tumors that often show overlapping morphologic features and immunohistochemical profiles. The increasing use of molecular testing in these tumors has enabled a better appreciation of their pathobiology, resulting in a wave of emerging neoplasms and improved characterization of ones previously considered exceptionally rare. Identification of specific molecular alterations has permitted targeted therapy options in tumors that were typically unresponsive to conventional therapies, as well as recognition that a subset can have a hereditary basis. This review will discuss the more "common" of the uncommon uterine mesenchymal neoplasms, including inflammatory myofibroblastic tumor, perivascular epithelioid cell tumor, uterine tumor resembling ovarian sex cord tumor, and embryonal rhabdomyosarcoma. This will be followed by an overview of emerging entities, including NTRK-rearranged uterine sarcoma, SMARCA4-deficient uterine sarcoma, KAT6B/A::KANSL1 fusion uterine sarcoma, and MEIS1::NCOA2/1 fusion sarcoma.

An Unusual Endometrial Stromal Neoplasm With JAZF1-BCORL1 Rearrangement.

Endometrial stromal tumors represent the second most common category of uterine mesenchymal tumors. Several different histologic variants and underlying genetic alterations have been recognized, one such being a group associated with BCORL1 rearrangements. They are usually high-grade endometrial stromal sarcomas, often associated with prominent myxoid background and aggressive behavior. Here, we report an unusual endometrial stromal neoplasm with JAZF1-BCORL1 rearrangement and briefly review the literature. The neoplasm formed a well-circumscribed uterine mass in a 50-yr-old woman and had an unusual morphologic appearance that did not warrant a high-grade categorization. It was characterized by a predominant population of epithelioid cells with clear to focally eosinophilic cytoplasm growing in interanastomosing cords and trabeculae set in a hyalinized stroma as well as nested and fascicular growths imparting focal resemblance to a uterine tumor resembling ovarian sex-cord tumor, PEComa, and a smooth muscle neoplasm. A minor storiform growth of spindle cells reminiscent of the fibroblastic variant of low-grade endometrial stromal sarcoma was also noted but conventional areas of low-grade endometrial stromal neoplasm were not identified. This case expands the spectrum of morphologic features seen in endometrial stromal tumors, especially when associated with a BCORL1 fusion and highlights the utility of immunohistochemical and molecular techniques in the diagnosis of these tumors, not all of which are high grade.

Diffuse Pediatric-type High-grade Glioma Arising in an Ovarian Mature Cystic Teratoma.

Immature neuroectodermal tissue can be found in the ovary as part of an immature teratoma or as part of a teratoma with malignant neuroectodermal transformation. Such lesions may closely resemble central nervous system tumors, but their biologic similarity is unclear. We describe an 18-yr-old female who presented with abdominal pain caused by an ovarian mass with widespread metastases. Histology showed a primitive, high-grade tumor arising in the background of a mature teratoma. The tumor was SOX10 positive, with focal expression of GFAP, S100, NSE, and synaptophysin. Molecular analysis demonstrated co-amplification of PDGFRA and KIT , alterations common in high-grade gliomas. By whole-genome methylation profiling, it clustered into the "diffuse pediatric-type high-grade glioma, RTK1 subtype, subclass c" group. Despite progressing through 2 lines of chemotherapy with widespread metastatic disease, she achieved an excellent response to chemotherapy directed toward aggressive germ cell tumors. This case emphasizes the importance of immunohistochemical, genomic, and epigenetic analyses to accurately classify these exceedingly rare tumors and determine the optimal therapy.

Clinicopathologic Evaluation and Molecular Profiling of Recurrent Stage IA Endometrial Endometrioid Carcinoma: A Case-control Study.

Most low-grade, early-stage endometrial endometrioid carcinomas (EEC) have an excellent prognosis; however, recurrences occur in a small subset with several studies reporting an increase in CTNNB1 exon 3 mutations in this population. Herein we evaluated 10 recurrent low-grade (FIGO 1 or 2), early-stage (FIGO IA) EECs matched to 10 nonrecurrent EECs to further characterize their clinicopathologic features and molecular phenotype. Cases were matched to controls based on size, grade, and depth of invasion. All tumors were evaluated for specific clinicopathologic parameters followed by next-generation sequencing using a 1213 gene panel. Recurrent EECs demonstrated no significant clinicopathologic differences when compared with nonrecurrent EECs, in terms of age, body mass index, pattern of invasion, presence of endometrial atypical hyperplasia/endometrioid intraepithelial neoplasia, associated metaplastic changes, peritumoral lymphocytes, mitoses, and tumor-infiltrating lymphocytes. Both cohorts also showed a similar number of pathogenic mutations, including CTNNB1 exon 3 mutations, as well as tumor mutational burden and microsatellite profiles. Although in this particular study, the lack of correlation between CTNNB1 exon 3 mutation and recurrence might be secondary to a small sample size, it also suggests the presence of other contributing factors. Thus, it helps set the foundation for larger series incorporating whole genome, transcriptome, proteome, and epigenome analyses to answer this clinically important question.

Uterine PEComas: correlation between melanocytic marker expression and TSC alterations/TFE3 fusions.

Uterine PEComas often present a diagnostic challenge as they share morphological and immunohistochemical features with smooth muscle tumors. Herein we evaluated a series of 19 uterine PEComas to compare the degree of melanocytic marker expression with their molecular profile. Patients ranged from 32-77 (median 48) years, with six tumors classified as malignant based on the modified gynecologic-specific prognostic algorithm. All patients with malignant PEComas were alive with disease or dead  of disease at last follow-up, while all those of uncertain malignant potential were alive and well (median follow-up, 47 months).Seventeen of 19 (89%) PEComas harbored either a TSC1 or TSC2 alteration. One of the two remaining tumors showed a TFE3 rearrangement, but the other lacked alterations in all genes evaluated. All showed at least focal (usually strong) positivity for HMB-45, with 15/19 (79%) having >50% expression, while the tumor lacking TSC or TFE3 alterations was strongly positive in 10% of cells. Melan-A and MiTF were each positive in 15/19 (79%) tumors, but staining extent and intensity were much more variable than HMB-45. Five of six (83%) malignant PEComas also harbored alterations in TP53, ATRX, or RB1, findings not identified in any tumors of uncertain malignant potential. One malignant PEComa was microsatellite-unstable/mismatch repair protein-deficient.In summary, TSC alterations/TFE3 fusions and diffuse (>50%) HMB-45 expression are characteristic of uterine PEComas. In morphologically ambiguous mesenchymal neoplasms with myomelanocytic differentiation, especially those with metastatic or recurrent disease, next-generation sequencing is recommended to evaluate for TSC alterations; as such, patients can be eligible for targeted therapy.

Crowdsourcing biocuration: The Community Assessment of Community Annotation with Ontologies (CACAO).

Experimental data about gene functions curated from the primary literature have enormous value for research scientists in understanding biology. Using the Gene Ontology (GO), manual curation by experts has provided an important resource for studying gene function, especially within model organisms. Unprecedented expansion of the scientific literature and validation of the predicted proteins have increased both data value and the challenges of keeping pace. Capturing literature-based functional annotations is limited by the ability of biocurators to handle the massive and rapidly growing scientific literature. Within the community-oriented wiki framework for GO annotation called the Gene Ontology Normal Usage Tracking System (GONUTS), we describe an approach to expand biocuration through crowdsourcing with undergraduates. This multiplies the number of high-quality annotations in international databases, enriches our coverage of the literature on normal gene function, and pushes the field in new directions. From an intercollegiate competition judged by experienced biocurators, Community Assessment of Community Annotation with Ontologies (CACAO), we have contributed nearly 5,000 literature-based annotations. Many of those annotations are to organisms not currently well-represented within GO. Over a 10-year history, our community contributors have spurred changes to the ontology not traditionally covered by professional biocurators. The CACAO principle of relying on community members to participate in and shape the future of biocuration in GO is a powerful and scalable model used to promote the scientific enterprise. It also provides undergraduate students with a unique and enriching introduction to critical reading of primary literature and acquisition of marketable skills.

Perivascular epithelioid cell tumors (PEComa) of the gynecologic tract.

PEComas of the female genital tract are rare mesenchymal neoplasms that are most common in the uterus, but also may occur in other gynecologic locations. As they morphologically and immunohistochemically resemble smooth muscle tumors, distinction between the two entities is often challenging, and may be aided by molecular analysis. Thus far, two distinct molecular groups-classic PEComas with TSC mutations and TFE3-translocation associated PEComas with TFE3 fusions have been described. Recognition of the first group is imperative as these patients may benefit from targeted therapy with mTOR inhibitors, if malignant. This review will focus on recognition of the morphologic and immunophenotypic features of PEComas, as well as the role of molecular testing in their diagnosis and treatment, analysis of the different algorithms to predict behavior, and differential diagnosis.

Uterine inflammatory myofibroblastic tumor: First report of a ROS1 fusion.

Inflammatory myofibroblastic tumor (IMT) of the uterus is an uncommon mesenchymal neoplasm that frequently harbors ALK rearrangements. In this report, we describe the first uterine IMT with a FN1-ROS1 fusion, which occurred in a 43-year-old woman who presented with menorrhagia. Morphologically, the well-circumscribed 3 cm tumor was comprised of compact and myxoid foci of relatively bland spindle cells admixed with scattered chronic inflammatory cells limited to the myxoid areas. ROS1 showed moderate cytoplasmic granular staining in < 30% of cells in the myxoid foci, while ALK was negative. RNA sequencing detected a FN1-ROS1 rearrangement that fused FN1 exon 37 to ROS1 exon 34. Although non-ALK-rearranged uterine IMTs are exceedingly rare, this example highlights the importance of performing ROS1 immunohistochemistry and/or molecular analysis in ALK-negative uterine neoplasms morphologically compatible with IMT.

Recurrent MEIS1-NCOA2/1 fusions in a subset of low-grade spindle cell sarcomas frequently involving the genitourinary and gynecologic tracts.

Sarcomas with MEIS1-NCOA2 fusions have been so far reported in 2 cases each of primitive renal sarcomas and intraosseous pelvic rhabdomyosarcomas. Their histologic spectrum, anatomic distribution, and clinical behavior remain poorly defined. In this study, we report 6 additional spindle cell sarcomas with MEIS1-NCOA2 or NCOA1 fusions that fall into the same disease spectrum with the previously reported renal sarcomas. The patients' age range was wide (20-76 years, mean 46) and all except one were female. The tumors arose in the kidney (n = 2), and one each in the uterine corpus, vagina, scrotum, and para-rectal region. The consistent morphology was that of monomorphic spindle to ovoid cells in a storiform, whorling, or solid pattern. Alternating cellularity, myxoid stroma, and microcystic changes were seen in some cases. Mitotic activity varied greatly (<1-33/10 high power fields). The immunophenotype was nonspecific, with most cases expressing variable degrees of TLE1, WT1, cyclin D1, CD56, and CD10. Using various platforms of RNA-based targeted sequencing, MEIS1-NCOA2 fusions were recurrently identified in 5 cases, and a novel MEIS1-NCOA1 fusion was found in one renal tumor. The gene fusions were validated by fluorescence in situ hybridization using custom BAC probes. Of the 5 patients with available follow-up (5 months to 8 years), all experienced local recurrences, but no distant spread or death from disease. Our results expand the clinicopathologic spectrum of sarcomas with MEIS1-NCOA2/1 fusions, providing evidence of an undifferentiated spindle cell phenotype with nonspecific immunoprofile and low-grade clinical behavior.

Embryonal rhabdomyosarcoma of the uterine corpus: a clinicopathological and molecular analysis of 21 cases highlighting a frequent association with DICER1 mutations.

Herein we evaluated a series of 21 embryonal rhabdomyosarcomas of the uterine corpus (ucERMS), a rare neoplasm, to characterize their morphology, genomics, and behavior. Patients ranged from 27 to 73 (median 52) years and tumors from 4 to 15 (median 9) cm, with extrauterine disease noted in two. Follow-up (median 16 months) was available for 14/21 patients; nine were alive and well, four died of disease, and one died from other causes. Most tumors (16/21) showed predominantly classic morphology, comprised of alternating hyper- and hypocellular areas of primitive small cells and differentiating rhabdomyoblasts in a loose myxoid/edematous stroma. A cambium layer was noted in all; seven had heterologous elements (six with fetal-type cartilage) and eight displayed focal anaplasia. The remaining five neoplasms showed only a minor component (≤20%) of classic morphology, with anaplasia noted in four and tumor cell necrosis in three. The most frequent mutations detected were in DICER1 (14/21), TP53 (7/20), PI3K/AKT/mTOR pathway (7/20), and KRAS/NRAS (5/20). Copy-number alterations were present in 10/19 tumors. Overall, 8/14 DICER1-associated ucERMS showed concurrent loss of function and hotspot mutations in DICER1, which is a feature more likely to be seen in tumors associated with DICER1 syndrome. Germline data were available for two patients, both DICER1 wild type (one with concurrent loss of function and hotspot alterations). DICER1-associated ucERMS were more likely to show a classic histological appearance including heterologous elements than DICER1-independent tumors. No differences in survival were noted between the two groups, but both patients with extrauterine disease at diagnosis and two with recurrences died from disease. As no patients had a known personal or family history of DICER1 syndrome, we favor most DICER1-associated ucERMS to be sporadic.

Evaluation of SWI/SNF Protein Expression by Immunohistochemistry in Ovarian Clear Cell Carcinoma.

Ovarian clear cell carcinomas (OCCC) are known to harbor ARID1A mutations, and several recent studies have described immunohistochemical loss of SMARCA2, SMARCA4, and SMARCB1 in a subset of tumors. We performed ARID1A, SMARCA2, SMARCA4, and SMARCB1 immunohistochemistry on 105 OCCCs to identify possible associations with clinicopathologic features and assess their prognostic value in these tumors. ARID1A, SMARCA4, and SMARCB1 were considered retained if any tumor cell nucleus stained while for SMARCA2, >5% of tumor nuclei were required to be positive. Patients had a mean age of 56 yr and tumors averaged 13 cm in size. Most patients (63%) had stage I tumors with 47% being alive and well, 41% dead from disease, 10% dead from other causes, and 3% alive with disease at last follow-up (mean 72 mo). Tumors showed an admixture of architectural patterns, but papillary was most frequent (49%). Stromal hyalinization was detected in 83% of OCCCs and a background precursor in 78%. High-grade atypia and/or oxyphilic cells were noted in 45% and 29% of tumors, respectively. All OCCCs expressed SMARCA4 and SMARCB1, but the absence of ARID1A was noted in 30% of tumors and SMARCA2 in 8%. ARID1A-retained OCCCs were associated with a dominant tubulocystic or solid pattern, but no other clinicopathologic features reached statistical significance. No switch/sucrose non-fermentable protein expression was predictive of prognosis. Additional studies with known mutational status of these proteins are warranted to better assess their prognostic utility and develop a standardized immunohistochemical scoring system.

Clear Cell Papillary Cystadenoma of the Ovary Masquerading as Metastatic Clear Cell Renal Cell Carcinoma: A Case Report and Review of the Literature.

Clear cell papillary cystadenoma of the epididymis is an uncommon benign neoplasm, usually seen in patients with von Hippel-Lindau disease. Morphologic and immunohistochemical examination aid in distinguishing clear cell papillary cystadenoma from malignant histologic mimics including low-grade mesothelial proliferations and metastatic clear cell renal cell carcinomas. Analogous lesions have been described in the female genital tract, often posing diagnostic challenges due to their low incidence. Here, we present the difficult diagnostic aspects of the first case of clear cell papillary cystadenoma involving the ovary, including the salient immunohistochemical, ultrastructural, and molecular characteristics.

Undifferentiated and dedifferentiated neoplasms of the female genital tract.

Undifferentiated neoplasms in the female gynecologic tract comprise two main groups-undifferentiated carcinoma, most common in the endometrium and ovary, and undifferentiated uterine sarcoma, although tumors with an undifferentiated appearance may occur in all gynecologic organs. Their differential diagnosis is broad and generous sampling, careful morphological evaluation, judicious use of immunohistochemistry, and in many cases, molecular testing is often essential in the diagnostic work-up. As some of these neoplasms fail to respond to conventional chemotherapy regimens and/or radiation therapy, targeted therapy may be valuable in treating these highly aggressive tumors, thus the importance of precise diagnosis. In this review we discuss the clinicopathological features of undifferentiated carcinoma, dedifferentiated carcinoma, and undifferentiated uterine sarcoma, followed by a comprehensive analysis of morphological mimickers. Finally, we briefly review ovarian and lower genital tract tumors with an undifferentiated histological appearance.

Mesenchymal lesions of the vulva.

Mesenchymal lesions of the vulva include site-specific entities limited to the lower genital tract, as well as a range of non-site-specific tumors that are more common at extragenital sites. Site-specific lesions include fibroepithelial stromal polyp, cellular angiofibroma, angiomyofibroblastoma, and aggressive angiomyxoma. Non-site-specific tumors that may occur in the vulva include those of smooth muscle, skeletal muscle, vascular, neural, adipocytic, and uncertain differentiation. This review discusses both site-specific and non-site-specific vulvar mesenchymal lesions including non-neoplastic proliferations, benign neoplasms, locally aggressive neoplasms with a predilection for local recurrence, neoplasms of indeterminate biologic potential, and frankly malignant neoplasms with a high risk of distant metastasis and death. Accurate diagnosis is essential for proper management, and is facilitated by correlation with clinical findings and targeted application of immunohistochemical and molecular studies.

Female adnexal tumors of probable Wolffian origin: morphological, immunohistochemical, and molecular analysis of 15 cases.

Female adnexal tumors of probable Wolffian origin are rare and present a diagnostic challenge due to their morphological and immunohistochemical overlap with more common ovarian and broad ligament entities. We evaluated the morphological, immunohistochemical, and molecular features of 15 tumors of probable Wolffian origin. Patients ranged from 32 to 69 (mean 47) years and tumors from 1.8 to 30 (mean 10) cm. All except one arose in para-adnexal soft tissues. Follow-up was available for six patients, five of whom were alive and well, while the sixth, who had extra-adnexal disease at diagnosis, died from unrelated causes. The following patterns were noted: tubular (all tumors), solid 11/15 (73%), sieve-like 7/15 (47%), and reticular 1/15 (7%). A myxoid background was present in 3/15 (20%) of tumors and eosinophilic luminal secretions in 11/15 (73%). Most tumors (12/15, 80%) had low-grade nuclear atypia, while three showed foci with scattered high-grade atypia. Mitotic index ranged from 0 to 17 (mean 4) per ten high-power fields. Tumors were positive for pankeratin and negative for TTF-1. EMA, GATA3, and PAX8 were positive in 2/10 (20%; focal), 3/15 (20%; focal), and 1/15 (7%; focal) of tumors, respectively. CD10, SF-1, calretinin, inhibin, ER, PR, cytokeratin 7, and WT1 were variably expressed. Pathogenic mutations were rare and included STK11 (n = 3), APC (n = 1), and MBD4 (n = 1). Copy number variations were detected in the three tumors with STK11 mutations and a myxoid background. These data demonstrate that female adnexal tumors of probable Wolffian origin are morphologically and immunohistochemically diverse, but infrequently harbor pathogenic mutations. However, their lack of mutations in contrast to their mimickers may be a valuable tool in diagnostically difficult cases.

Protein Expression Profiles among Lichen Sclerosus Urethral Strictures-Can Urethroplasty Success be Predicted?

PURPOSE: Urethroplasty of lichen sclerosus strictures has a significantly higher failure rate than strictures due to other causes. We sought to determine predictors of urethroplasty failure in men with lichen sclerosus urethral stricture disease by evaluating protein expression profiles. MATERIALS AND METHODS: Urethral tissue was excised from patients with lichen sclerosus who were undergoing urethroplasty of urethral stricture disease at a single institution. A tissue microarray was created with cores from each sample. Immunohistochemistry was performed to compare protein expression related to inflammation, cell cycle disruption, oxidative stress, hormone receptor status and infection. Stricture recurrence was defined by the need for a subsequent unanticipated procedure for urethral stricture disease. RESULTS: We evaluated 50 men with lichen sclerosus urethral stricture disease, including 31 with successful reconstruction and 19 with recurrent stricture. Recurrent strictures expressed lower levels of several inflammatory markers and had a lower Ki-67 mitotic index and significantly higher vascular endothelial growth factor levels than nonrecurrent strictures. CONCLUSIONS: To our knowledge this is the first study to use tissue protein expression to identify risk factors for urethroplasty failure among men with lichen sclerosus urethral stricture disease. Our findings suggest that recurrent lichen sclerosus strictures demonstrate a suppressed inflammatory response, a decreased cell turnover rate, and poor oxygenation and nutrient delivery. Prospective studies are needed to clarify the role of these pathways in the pathophysiology of lichen sclerosus urethral stricture disease, determine whether preoperative biopsy can predict urethroplasty success, help counsel patients and develop future treatments.

Ovarian Metastases of Breast Cancers With Signet Ring Cells: A Report of 17 Cases Including 14 Krukenberg Tumors.

Krukenberg tumor, defined as metastatic adenocarcinoma to the ovary containing at least 10% signet ring cells, usually arises from the stomach but can also originate from other sites. We reviewed 17 metastatic breast carcinomas to the ovary with signet ring cells to potentially identify features indicative of mammary origin as opposed to other possible primary sites. The patients ranged from 41 to 76 (mean, 53.6) yr. Fourteen had a prior history of invasive breast carcinoma (invasive ductal carcinoma, 4; invasive lobular carcinoma, 3; adenocarcinoma not otherwise specified, 3; carcinoma with ductal and lobular features, 2; and unspecified carcinoma, 2) and metastases were identified 2 to 284 (mean, 79) mo after the original diagnosis. Three patients had no known history of invasive breast carcinoma: 1 was subsequently diagnosed with invasive lobular carcinoma, 1 had suspicious bilateral breast masses identified on imaging, and 1 was lost to follow-up. Bilateral ovarian metastases were present in 87%, and the tumors ranged from 3.8 to 19 (mean, 8) cm. Microscopically the ovarian architecture was effaced in 71% by discrete tumor lobules separated by striking edema. The tumors exhibited a variety of histologic patterns: nests were most common (88%), followed by cords (82%), diffuse sheets (82%), single cells (71%), small clusters (41%), glands (29%), and follicle-like cysts (12%). Signet ring cells comprised 2% to 70% (mean, 33%) of the tumors, with 14 cases meeting the criteria for Krukenberg tumor. Signet ring cells were most frequently observed within diffuse sheets (71%) and cords (65%). Tumor cells arranged in nests, cords, and diffuse sheets are typical of Krukenberg tumor of breast origin, and the patterns recapitulate those seen in primary breast carcinomas. Features characteristic of gastrointestinal origin, such as extracellular mucin, intestinal-type glands, dirty necrosis, microcysts, and goblet cell carcinoid-like foci, were absent. The overall morphologic picture in cases of ovarian spread of breast cancer with signet ring cells is usually strongly suggestive of mammary origin. The diagnosis can be further supported by the clinical history and immunohistochemical evaluation.

Inflammatory myofibroblastic tumor of the uterus: a clinicopathological, immunohistochemical, and molecular analysis of 13 cases highlighting their broad morphologic spectrum.

Inflammatory myofibroblastic tumors of the uterus are rare, and although most have a favorable prognosis, a small subset exhibit extrauterine disease, recur, or cause death. In this study, we evaluated the morphology and immunoprofile of 13 uterine inflammatory myofibroblastic tumors, including four with aggressive behavior. ALK rearrangements were detected by fluorescence in situ hybridization and fusion partners by anchored multiplex assay. Patients ranged from 8 to 63 (mean 39) years and tumors from 2.5 to 20 (mean 7.4) cm. Myxoid, compact, and hyalinized patterns were noted in 13, 12, and 2 tumors, ranging from 1 to 100%, 5 to 99%, and 0 to 5%, respectively. Nuclear atypia was mild in six (46%), moderate in five (38%), and severe in two (15%), with ganglion-like cells in two tumors. Mitoses ranged from 0 to 24 (mean 5) per 10 high-power fields. Inflammation was mild in five (38%), moderate in three (23%), and marked in five (38%), consisting of a lymphoplasmacytic infiltrate that was lymphocyte-predominant in six (46%). Lymphovascular invasion was noted in two (15%) and necrosis in eight (62%). All but one tumor were ALK-positive by immunohistochemistry, with granular cytoplasmic staining in nine (82%). ALK rearrangements (tested in 10) were detected in eight and was absent in one. The remaining tumor showed an isolated green 5' ALK signal. Fusion partners were identified in 10 (77%) and included THBS1 (n=3), IGFBP5 (n=2), DES (n=2), SEC31 (n=1), TPM3 (n=1), and TIMP3 (n=1). Size ≥8 cm was predictive of aggressive behavior (P<0.01), with increased mitoses (≥7 per 10 high-power fields), lymphovascular invasion, and compact-predominance approaching statistical significance. These data show that inflammatory myofibroblastic tumors of the uterus are morphologically heterogenous with frequent ALK expression and a variety of ALK fusion partners. Recognition of this rare mesenchymal neoplasm is crucial as those with aggressive behavior can potentially be treated with tyrosine kinase inhibitors.