DICER1 mutations are frequent in müllerian adenosarcomas and are independent of rhabdomyosarcomatous differentiation

p160 nuclear receptor coactivator family members and their role in rare fusion‑driven neoplasms (Review)

Gene fusions with translocations involving nuclear receptor coactivators (NCoAs) are relatively common among fusion-driven malignancies. NCoAs are essential mediators of environmental cues and can modulate the transcription of downstream target genes upon binding to activated nuclear receptors. Therefore, fusion proteins containing NCoAs can become strong oncogenic drivers, affecting the cell transcriptional profile. These tumors show a strong dependency on the fusion oncogene; therefore, the direct pharmacological targeting of the fusion protein becomes an attractive strategy for therapy. Currently, different combinations of chemotherapy regimens are used to treat a variety of NCoA-fusion-driven tumors, but given the frequent tumor reoccurrence, more efficient treatment strategies are needed. Specific approaches directed towards inhibition or silencing of the fusion gene need to be developed while minimizing the interference with the original genes. This review highlights the relevant literature describing the normal function and structure of NCoAs and their oncogenic activity in NCoA-gene fusion-driven cancers, and explores potential strategies that could be effective in targeting these fusions.

Familial syndromes associated with testicular and paratesticular neoplasms: a comprehensive review

A syndromic association between a subset of testicular/paratesticular neoplasms is well established. Such examples include Carney complex and large cell calcifying Sertoli cell tumor, Peutz-Jeghers syndrome and intratubular large cell hyalinizing Sertoli cell neoplasia, and VHL syndrome and clear cell papillary cystadenoma of the epididymis.However, recent studies proposed potential novel links between some testicular and paratesticular neoplasms with certain tumor syndromes. While more studies are still needed to solidify these associations, recent research suggests that a subset of Leydig cell tumors may arise in patients with hereditary leiomyomatosis and renal cell carcinoma syndrome or that some seminomas may occur in Lynch syndrome patients. Additionally, an association between testicular sex cord stromal tumors and paratesticular sarcomas with Familial adenomatous polyposis syndrome and DICER1 syndrome, respectively, has been proposed as well. This review provides a comprehensive overview of the intricate relationship between familial syndromes and associated testicular and paratesticular tumors, shedding light on their clinicopathological and molecular characteristics.

[Diagnosis of uterine sarcomas and rare uterine mesenchymal tumours with malignant potential. Guidelines of the French Sarcoma Group and Rare Gynaecological Tumours]

The landscape of uterine sarcomas is becoming more complex with the description of new entities associated with recurrent driver molecular alterations. Uterine sarcomas, in analogy with soft tissue sarcomas, are distinguished into complex genomic and simple genomic sarcomas. Leiomyosarcomas and undifferentiated uterine sarcomas belong to complex genomic sarcomas group. Low-grade and high-grade endometrial stromal sarcomas, other rare tumors associated with fusion transcripts (such as NTRK, PDGFB, ALK, RET ROS1) and SMARCA4-deficient uterine sarcoma are considered simple genomic sarcomas. The most common uterine sarcoma are first leiomyosarcoma and secondly endometrial stromal sarcomas. Three different histological subtypes of leiomyosarcoma (fusiform, myxoid, epithelioid) are identified, myxoid and epithelioid leiomyosarcoma being more aggressive than fusiform leiomyosarcoma. The distinction between low-grade and high-grade endometrial stromal sarcoma is primarily morphological and immunohistochemical and the detection of fusion transcripts can help the diagnosis. Uterine PEComa is a rare tumor, which is distinguished into borderline and malignant, according to a risk assessment algorithm. Embryonal rhabdomyosarcoma of the uterine cervix is more common in children but can also occur in adult women. Embryonal rhabdomyosarcoma of the uterine cervix is almost always DICER1 mutated, unlike that of the vagina which is wild-type DICER1, and adenosarcoma which can be DICER1 mutated but with less frequency. Among the emerging entities, sarcomas associated with fusion transcripts involving the NTRK, ALK, PDGFB genes benefit from targeted therapy. The integration of molecular data with histology and clinical data allows better identification of uterine sarcomas in order to better treat them.

Biallelic Dicer1 Mutations in the Gynecologic Tract of Mice Drive Lineage-Specific Development of DICER1 Syndrome-Associated Cancer

DICER1 is an RNase III enzyme essential for miRNA biogenesis through cleaving precursor-miRNA hairpins. Germline loss-of-function DICER1 mutations underline the development of DICER1 syndrome, a rare genetic disorder that predisposes children to cancer development in organs such as lung, gynecologic tract, kidney, and brain. Unlike classical tumor suppressors, the somatic "second hit" in DICER1 syndrome-associated cancers does not fully inactivate DICER1 but impairs its RNase IIIb activity only, suggesting a noncanonical two-hit hypothesis. Here, we developed a genetically engineered conditional compound heterozygous Dicer1 mutant mouse strain that fully recapitulates the biallelic DICER1 mutations in DICER1 syndrome-associated human cancers. Crossing this tool strain with tissue-specific Cre strains that activate Dicer1 mutations in gynecologic tract cells at two distinct developmental stages revealed that embryonic biallelic Dicer1 mutations caused infertility in females by disrupting oviduct and endometrium development and ultimately drove cancer development. These multicystic tubal and intrauterine tumors histologically resembled a subset of DICER1 syndrome-associated human cancers. Molecular analysis uncovered accumulation of additional oncogenic events (e.g., aberrant p53 expression, Kras mutation, and Myc activation) in murine Dicer1 mutant tumors and validated miRNA biogenesis defects in 5P miRNA strand production, of which, loss of let-7 family miRNAs was identified as a putative key player in transcriptomic rewiring and tumor development. Thus, this DICER1 syndrome-associated cancer model recapitulates the biology of human cancer and provides a unique tool for future investigation and therapeutic development.

SIGNIFICANCE

Generation of a Dicer1 mutant mouse model establishes the oncogenicity of missense mutations in the DICER1 RNase IIIb domain and provides a faithful model of DICER1 syndrome-associated cancer for further investigation.

Uterine Tumor Resembling Ovarian Sex Cord Tumors: 23 Cases Indicating Molecular Heterogeneity With Variable Biological Behavior

Uterine tumor resembling ovarian sex cord tumor (UTROSCT) is a rare mesenchymal neoplasm that mainly harbors NCOA1-3 rearrangements with partner genes ESR1 or GREB1 . Here, we explored 23 UTROSCTs by targeted RNA sequencing. The association between molecular diversity and clinicopathologic features was investigated. The mean age of our cohort was 43 years (23-65 y). Only 15 patients (65%) were originally diagnosed with UTROSCTs. Mitotic figures ranged from 1 to 7/10 high power fields, of primary tumors and increased from 1 to 9/10 high power fields in recurrent tumors. Five types of gene fusions were identified in these patients, including GREB1::NCOA2 (n=7), GREB1::NCOA1 (n=5), ESR1::NCOA2 (n=3), ESR1::NCOA3 (n=7), and GTF2A1::NCOA2 (n=1). To our knowledge, our group included the largest cohort of tumors with GREB1::NCOA2 fusions. Recurrences were most common in patients with GREB1::NCOA2 fusion (57%), followed by 40% ( GREB1::NCOA1 ), 33% ( ESR1::NCOA2 ), and 14% ( ESR1::NCOA3 ). The recurrent patient who harbored an ESR1::NCOA2 fusion was characterized by extensive rhabdoid features. Both of the recurrent patients who harbored GREB1::NCOA1 and ESR1::NCOA3 had the largest tumor sizes in their own gene alteration groups, and another recurrent GREB1::NCOA1 patient had extrauterine involvement. The GREB1 -rearranged patients were of older age, larger tumor size, and higher stage than non- GREB1 -rearranged patients ( P =0.004, 0.028, and 0.016, respectively). In addition, the GREB1 -rearranged tumors presented more commonly as intramural masses rather than non- GREB1 -rearranged tumors presenting as polypoid/submucosal masses ( P =0.021). Microscopically, nested and whorled patterns were frequently seen in GREB1- rearranged patients ( P =0.006). Of note, estrogen receptor expression was weaker than progesterone receptor in all 12 GREB1- rearranged tumors, whereas the similar staining intensity of estrogen receptor and progesterone receptor was observed in all 11 non- GREB1- rearranged tumors ( P <0.0001). This study demonstrated that UTROSCTs were present at a younger age in the Chinese population. The genetic heterogeneity of UTROSCTs was correlated with variable recurrence rate. Tumors with GREB1::NCOA2 fusions are more likely to recur compared with those with other genetic alterations.

ATM mutation in aggressive uterine adenosarcoma in which systemic chemotherapies had remarkable effects

Uterine adenosarcoma is a rare gynecologic malignancy, and 10-25% of the cases exhibit clinically aggressive behaviors. Although TP53 mutations are frequently identified in high-grade adenosarcomas of the uterus, definitive gene alterations have not been identified in uterine adenosarcomas. Specifically, no reports have described mutations in homologous recombination deficiency-related genes in uterine adenosarcomas. This study presents a case of uterine adenosarcoma without sarcomatous overgrowth but with TP53 mutation that exhibited clinically aggressive behaviors. The patient had an ATM mutation, which is a gene associated with homologous recombination deficiency, and exhibited a good response against platinum-based chemotherapy and possible therapeutic target by poly(ADP-ribose) polymerase inhibitors.

From Malignant Thyroid Teratoma to Thyroblastoma: Evolution of a Newly-recognized DICER1 -associated Malignancy

Thyroblastoma is a novel thyroid malignancy included in the 5th Edition WHO Classification of Endocrine and Neuroendocrine Tumours. The majority of tumors now classified as thyroblastoma were originally regarded to be malignant thyroid teratomas. However, these neoplasms were recently recognized as a separate entity based on a distinctive constellation of primitive multilineage elements, including immature thyroid epithelium, undifferentiated or rhabdomyoblastic spindle cell proliferations, and neuroepithelial blastema, as well as recurrent DICER1 hotspot mutations. Thyroblastoma is an aggressive tumor that leads to death from disease in ~50% of patients, making it essential to differentiate this entity from a wide range of other thyroid tumors that show overlapping histologic features or DICER1 mutations. This review aims to provide a practical overview of the background, clinicopathologic features, molecular underpinnings, and differential diagnosis of this recently-described and molecularly-defined entity.

Mullerian adenosarcoma: clinicopathologic and molecular characterization highlighting recurrent BAP1 loss and distinctive features of high-grade tumors

Mullerian adenosarcoma is an uncommon mesenchymal tumor of the gynecologic tract. Most cases are low-grade, while high-grade adenosarcomas are rare and not well studied. Herein, we characterize the clinicopathologic and molecular features of 27 adenosarcomas of gynecologic origin, enriched for high-grade tumors subjected to targeted panel sequencing. Sarcomatous overgrowth was more frequently seen in high-grade compared to low-grade tumors (12/17, 71%, vs 1/10, 10%, p = 0.004) and heterologous elements were exclusive to high-grade cases (n = 7, p = 0.03). All deaths were from high-grade disease (advanced primary, n = 2, or recurrence, n = 5). Genetic alterations specific to high-grade adenosarcomas have known associations with chromosome instability, including TP53 mutations (n = 4) and amplifications of MDM2 (n = 2) and CCNE1 (n = 2). Somatic ATRX frameshift mutations were found in 2 patients with high-grade recurrences following a primary low-grade adenosarcoma and ATRX deletion in 1 high-grade adenosarcoma with an adjacent low-grade component. The fraction of genome altered by copy number alterations was significantly higher in high-grade compared to low-grade adenosarcomas (P = 0.001). Other recurrent genetic alterations across the entire cohort included BAP1 homozygous deletions (n = 4), DICER1 mutations (n = 4), ARID1A mutations (n = 3), TERT promoter mutations (n = 2) and amplification (n = 1), as well as alterations involving members of the PI3K and MAPK signaling pathways. One tumor harbored an ESR1-NCOA3 fusion and another had an MLH1 homozygous deletion. Immunohistochemical analysis for BAP1 revealed loss of nuclear expression in 6/24 (25%) cases, including all four tumors with BAP1 deletions. Notably, out of 196 mesenchymal neoplasms of gynecologic origin, BAP1 homozygous deletion was only found in adenosarcomas (P = 0.0003). This study demonstrates that high-grade adenosarcomas are heterogeneous at the molecular level and are characterized by genomic instability and TP53 mutations; ATRX loss may be involved in high-grade transformation of low-grade adenosarcoma; and BAP1 inactivation appears to be a specific pathogenic driver in a subset of adenosarcomas.

DICER1-associated Tumors in the Female Genital Tract: Molecular Basis, Clinicopathologic Features, and Differential Diagnosis

DICER1 syndrome is a tumor predisposition syndrome in which patients are at an increased risk of developing a wide variety of benign and malignant neoplasms with a hallmark constellation of pediatric pleuropulmonary blastoma, cystic nephroma, and thyroid lesions. DICER1 encodes an RNA endoribonuclease that is crucial to the processing of microRNA and may play a role in the maturation of Müllerian tissue. Within the gynecologic tract, germline mutations in DICER1 are associated with an array of rare tumors, including Sertoli-Leydig cell tumor, embryonal rhabdomyosarcoma of the cervix, gynandroblastoma, and juvenile granulosa cell tumor, which typically present in childhood, adolescence, or early adulthood. In addition, somatic DICER1 mutations have been described in rare gynecologic tumors such as adenosarcoma, Sertoli cell tumor, ovarian fibrosarcoma, cervical primitive neuroectodermal tumor, carcinosarcoma, and germ cell tumors. In light of the significant association with multiple neoplasms, genetic counseling should be considered for patients who present with a personal or family history of these rare DICER1-associated gynecologic tumors. This review highlights the most current understanding of DICER1 genetic alterations and describes the clinical, histopathologic, and immunohistochemical features and differential diagnoses for gynecologic tumors associated with DICER1 mutation.

Embryonal Rhabdomyosarcoma of the Uterine Cervix: A Clinicopathologic Study of 94 Cases Emphasizing Issues in Differential Diagnosis Staging, and Prognostic Factors

Embryonal rhabdomyosarcoma of the uterine cervix (cERMS) is rare and frequently associated with DICER1 mutations. We report 94 tumors that arose in patients aged 7 to 59 (median=23) years and presented with vaginal bleeding (52), protruding vaginal mass (17), cervical polyp (8), or expelled tumor fragments per vagina (5). Nine had DICER1 syndrome, 8 of whom had other syndromic manifestations including ovarian Sertoli-Leydig cell tumor (7), multinodular goiter (3), pleuropulmonary blastoma (2), pineoblastoma (1), and osteosarcoma (1). Syndromic patients were younger than nonsyndromic patients (16 vs. 24 y). Tumor size ranged from 2 to 24 (median=4.5) cm. Ninety-two tumors were polypoid, most being grape-like (77 of 92). They were characterized by aggregates of primitive cells, almost always exhibiting a cambium layer, within a variably myxoedematous stroma and were hypocellular (63), moderately cellular (22), or hypercellular (9). Entrapped glands, typically scant, were present in 84 tumors. Primitive hyperchromatic ovoid to spindled cells with minimal cytoplasm predominated but differentiated rhabdomyoblasts with abundant eosinophilic cytoplasm (having cross-striations in 30) were seen in 83 tumors; they were often sparse but predominated in three. Nine tumors showed areas of intersecting fascicles and 4 zones with densely cellular (solid) growth. Cartilage was present in 38. Anaplasia was seen in 15 tumors, as was necrosis. Mitotic activity ranged from 1 to 58/10 high-power fields (median=8). The varied microscopic features resulted in a spectrum of differential diagnostic considerations, mainly typical and cellular forms of fibroepithelial polyps, Mullerian adenosarcoma, and other sarcomas. Follow-up was available for 79 patients ranging from 6 to 492 (median=90) months. Treatment information was available in 62 and included polypectomy in 6 patients (2 also received chemotherapy), limited resection in 26 (14 also received chemotherapy), hysterectomy in 29 (15 with adjuvant chemotherapy), and biopsies only in 1 (with chemotherapy). Staging was possible in 56 tumors; according to the "uterine sarcoma" system (tumor size and extent) they were: stage I (10/56; could not be further subclassified as size not available), IA (22/56), IB (18/56), IIA (2/56), IIB 3/56), IIIC (1/56). According to the "adenosarcoma" system (depth of invasion and extent) they were: stage IA (26/56), IB (14/56), IC (10/56), IIA (2/56), IIB (3/56), IIIC (1/56). Eight patients had local recurrence following incomplete excision (10%). Eleven of 79 patients had extrauterine recurrences (14%) and 9 died of disease (11%). Older age was associated with extrauterine recurrence (median 44 vs. 22; P=0.002) and decreased disease-specific survival (median 44 vs. 22; P=0.02). For patients with tumors initially confined to the cervix, the adenosarcoma staging system was superior to the uterine sarcoma staging system for predicting survival (P=0.02). Three patients with DICER1 syndrome who underwent fertility-preserving surgery developed a second primary cERMS 7, 7, and 12 years after their primary tumor. All 9 patients with DICER1 syndrome had tumors confined to the cervix and none died of disease. This study highlights the intriguing clinical aspects of cERMS including its long-known tendency to occur in the young but also more recently appreciated association with DICER1 syndrome. Establishing the diagnosis may still be difficult because of the hazard of sampling a neoplasm which in areas may appear remarkably bland and also because of its potential confusion with other neoplasms. This study indicates that this tumor has a good prognosis at this site and in selected cases a conservative surgical approach is a realistic consideration.

DICER1-associated sarcoma of the aortic arch - a case report and literature review

Primary sarcoma of the aorta is extremely rare. We herein report a case of DICER1-associated sarcoma originating from the aortic arch. A 45-year-old male was admitted to the hospital with a cold left hand and weakened radial artery pulse in the left side. Computed tomography of the chest showed multiple penetrating ulcers with tumor-like ectasia at the aortic arch, diagnosed as a pseudoaneurysm. Histopathological analysis of the mass revealed a biphasic neoplasm composed of epithelial and mesenchymal components and a transition zone between the epithelial and mesenchymal cells, which supports the diagnosis of a biphasic sarcoma rather than carcinosarcoma. The differentiated cells of soft tissue showed strong and diffuse positivity for TLE-1, Bcl-2, and CD99; the nested epithelial cells were focally positive for CK-pan, but negative for EMA, membranous localization of β-catenin. This case showed a unique pattern of SS18-break-apart probe, with loss of the green signal (approximately 33%) by fluorescence in situ hybridization (FISH). Fusion gene profiling using whole transcriptome RNA sequencing (RNA-seq) indicated that this case was negative for common fusion genes including SS18. Next-generation sequencing (NGS) revealed somatic mutations in DICER1 . Taken together, this case was diagnosed as a DICER-associated biphasic sarcoma of the aortic arch. The patient died four months after aorta replacement therapy without radiotherapy and chemotherapy.

Phenotypic similarities within the morphologic spectrum of DICER1-associated sarcomas and pleuropulmonary blastoma: Histopathologic features guide diagnosis in the LMIC setting

Extrapulmonary DICER1-associated sarcomas (DS) can harbor morphological features overlapping with pleuropulmonary blastoma. We report three children with intracranial and genital tract sarcomas, suspected to have DS based on a heterogeneous yet defining combination of spindle-cell sarcomatous and blastemal morphology, with rhabdomyomatous differentiation. Foci of immature cartilage at diagnosis (n = 2/3) and increased neuroepithelial differentiation at recurrence (n = 1) were noted. Morphological suspicion prompted somatic testing at reference centers, confirming likely biallelic, loss-of-function, and "hotspot" missense DICER1 variants in all three tumors. This can serve as a model for this diagnosis in resource-limited settings and has implications for germline testing, surveillance, and tumor management.

Case Report: Uterine Adenosarcoma With Sarcomatous Overgrowth and Malignant Heterologous Elements

A 46- year-old woman presented a uterine adenosarcoma originating in the lower uterine segment. The diagnosis was made in an endometrial biopsy and confirmed in the pathological examination of the complete surgical specimen, both identifying heterologous malignant elements. In addition, complementary immunohistochemical studies were performed. We reviewed the literature, illustrating the clinical and morphological characteristics and the differential diagnoses to be evaluated.

Endometrial polyps are non-neoplastic but harbor epithelial mutations in endometrial cancer drivers at low allelic frequencies

Endometrial polyps (EMPs) are common exophytic masses associated with abnormal uterine bleeding and infertility. Unlike normal endometrium, which is cyclically shed, EMPs persist over ovulatory cycles and after the menopause. Despite their usual classification as benign entities, EMPs are paradoxically associated with endometrial carcinomas of diverse histologic subtypes, which frequently arise within EMPs. The etiology and potential origins of EMPs as clonally-derived neoplasms are uncertain, but previous investigations suggested that EMPs are neoplasms of stromal origin driven by recurring chromosomal rearrangements. To better define benign EMPs at the molecular genetic level, we analyzed individual EMPs from 31 women who underwent hysterectomy for benign indications. The 31 EMPs were subjected to comprehensive genomic profiling by exome sequencing of a large panel of tumor-related genes including oncogenes, tumor suppressors, and chromosomal translocation partners. There were no recurring chromosomal rearrangements, and copy-number analyses did not reveal evidence of significant chromosome-level events. Surprisingly, there was a high incidence of single nucleotide variants corresponding to classic oncogenic drivers (i.e., definitive cancer drivers). The spectrum of known oncogenic driver events matched that of endometrial cancers more closely than any other common cancer. Further analyses including laser-capture microdissection showed that these mutations were present in the epithelial compartment at low allelic frequencies. These results establish a link between EMPs and the acquisition of endometrial cancer driver mutations. Based on these findings, we propose a model where the association between EMPs and endometrial cancer is explained by the age-related accumulation of endometrial cancer drivers in a protected environment that-unlike normal endometrium-is not subject to cyclical shedding.

Atypical uterine polyps show morphologic and molecular overlap with mullerian adenosarcoma but follow a benign clinical course

A subset of clinically benign uterine polyps shows atypical morphologic features worrisome for, but not diagnostic of, Mullerian adenosarcoma. We report clinicopathologic data for 63 polyps from 58 women with atypical morphologic features including abnormal architecture, abnormal periglandular stroma, stromal atypia, and mitoses >2 per 10 hpf. Four (11%) of 36 women with follow-up tissue sampling had residual/recurrent atypical polyp. Twelve (27%) of 44 women underwent hysterectomy subsequent to a diagnosis of atypical polyp. No patient developed adenosarcoma over median follow-up of 150 months. Twenty-one primary atypical polyps underwent molecular profiling. Five (24%) harbored chr 12q13-15 gain or amplification, 9/20 (45%) harbored chr 6q25.1 gain, and 7/21 (33%) had no significant copy number alterations. Gains of chr 1q, chr 8p12, and chr 10q11.21-23, amplifications of chr 12q24.12-13, chr 15p24.1-26.1, and chr 18q21.33, and loss of chr 7 and chr 11q21 were each seen in a single polyp. Mean tumor mutational burden was 3.1 (range, 0.76-8.365) mutations/Mb. Pathogenic point mutations were identified in 12/20 (60%) primary atypical polyps. We propose the term "atypical uterine polyps" for these lesions, which show biologic overlap with early Mullerian adenosarcoma but lack molecular alterations characteristic of clinically aggressive adenosarcoma and appear to follow a benign clinical course. Conservative management with close clinical follow-up and repeat sampling can be considered for these lesions, when clinically appropriate.

Tumor Suppressor miRNA in Cancer Cells and the Tumor Microenvironment: Mechanism of Deregulation and Clinical Implications

MicroRNAs (miRNAs) are noncoding RNAs that have been identified as important posttranscriptional regulators of gene expression. miRNAs production is controlled at multiple levels, including transcriptional and posttranscriptional regulation. Extensive profiling studies have shown that the regulation of mature miRNAs expression plays a causal role in cancer development and progression. miRNAs have been identified to act as tumor suppressors (TS) or as oncogenes based on their modulating effect on the expression of their target genes. Upregulation of oncogenic miRNAs blocks TS genes and leads to tumor formation. In contrast, downregulation of miRNAs with TS function increases the translation of oncogenes. Several miRNAs exhibiting TS properties have been studied. In this review we focus on recent studies on the role of TS miRNAs in cancer cells and the tumor microenvironment (TME). Furthermore, we discuss how TS miRNA impacts the aggressiveness of cancer cells, with focus of the mechanism that regulate its expression. The study of the mechanisms of miRNA regulation in cancer cells and the TME may paved the way to understand its critical role in the development and progression of cancer and is likely to have important clinical implications in a near future. Finally, the potential roles of miRNAs as specific biomarkers for the diagnosis and the prognosis of cancer and the replacement of tumor suppressive miRNAs using miRNA mimics could be promising approaches for cancer therapy.

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.

Genomic alterations in gynecological malignancies: histotype-associated driver mutations, molecular subtyping schemes, and tumorigenic mechanisms

There are numerous histological subtypes (histotypes) of gynecological malignancies, with each histotype considered to largely reflect a feature of the "cell of origin," and to be tightly linked with the clinical behavior and biological phenotype of the tumor. The recent advances in massive parallel sequencing technologies have provided a more complete picture of the range of the genomic alterations that can persist within individual tumors, and have highlighted the types and frequencies of driver-gene mutations and molecular subtypes often associated with these histotypes. Several large-scale genomic cohorts, including the Cancer Genome Atlas (TCGA), have been used to characterize the genomic features of a range of gynecological malignancies, including high-grade serous ovarian carcinoma, uterine corpus endometrial carcinoma, uterine cervical carcinoma, and uterine carcinosarcoma. These datasets have also been pivotal in identifying clinically relevant molecular targets and biomarkers, and in the construction of molecular subtyping schemes. In addition, the recent widespread use of clinical sequencing for the more ubiquitous types of gynecological cancer has manifested in a series of large genomic datasets that have allowed the characterization of the genomes, driver mutations, and histotypes of even rare cancer types, with sufficient statistical power. Here, we review the field of gynecological cancer, and seek to describe the genomic features by histotype. We also will demonstrate how these are linked with clinicopathological attributes and highlight the potential tumorigenic mechanisms.

Genetic characterisation of adult primary pleomorphic uterine rhabdomyosarcoma and comparison with uterine carcinosarcoma

AIMS

To characterise the genetic alterations in adult primary uterine rhabdomyosarcomas (uRMSs) and to investigate whether these tumours are genetically distinct from uterine carcinosarcomas (UCSs).

METHODS AND RESULTS

Three tumours originally diagnosed as primary adult pleomorphic uRMS were subjected to massively parallel sequencing targeting 468 cancer-related genes and RNA-sequencing. Mutational profiles were compared with those of UCSs (n = 57) obtained from The Cancer Genome Atlas. Sequencing data analyses were performed using validated bioinformatic approaches. Pathogenic TP53 mutations and high levels of genomic instability were detected in the three cases. uRMS1 harboured a likely pathogenic YTHDF2-FOXR1 fusion. uRMS2 harboured a PPP2R1A hotspot mutation and amplification of multiple genes, including WHSC1L1, FGFR1, MDM2, and CCNE1, whereas uRMS3 harboured an FBXW7 hotspot mutation and an ANKRD11 homozygous deletion. Hierarchical clustering of somatic mutations and copy number alterations revealed that these tumours initially diagnosed as pleomorphic uRMSs and UCSs were similar. Subsequent comprehensive pathological re-review of the three uRMSs revealed previously unidentified minute pan-cytokeratin-positive atypical glands in one case (uRMS3), favouring its reclassification as UCS with extensive rhabdomyosarcomatous overgrowth.

CONCLUSIONS

Adult pleomorphic uRMSs harbour TP53 mutations and high levels of copy number alterations. Our findings underscore the challenge in discriminating between uRMS and UCS with rhabdomyosarcomatous differentiation.

The mutational repertoire of uterine sarcomas and carcinosarcomas in a Brazilian cohort: A preliminary study

OBJECTIVES

The present study aimed to contribute to the catalog of genetic mutations involved in the carcinogenic processes of uterine sarcomas (USs) and carcinosarcomas (UCSs), which may assist in the accurate diagnosis of, and selection of treatment regimens for, these conditions.

METHODS

We performed gene-targeted next-generation sequencing (NGS) of 409 cancer-related genes in 15 US (7 uterine leiomyosarcoma [ULMS], 7 endometrial stromal sarcoma [ESS], 1 adenosarcoma [ADS]), 5 UCS, and 3 uterine leiomyoma (ULM) samples. Quality, frequency, and functional filters were applied to select putative somatic variants.

RESULTS

Among the 23 samples evaluated in this study, 42 loss-of-function (LOF) mutations and 111 missense mutations were detected, with a total of 153 mutations. Among them, 66 mutations were observed in the Catalogue of Somatic Mutations in Cancer (COSMIC) database. TP53 (48%), ATM (22%), and PIK3CA (17%) were the most frequently mutated genes. With respect to specific tumor subtypes, ESS showed mutations in the PDE4DIP, IGTA10, and DST genes, UCS exhibited mutations in ERBB4, and ULMS showed exclusive alterations in NOTCH2 and HER2. Mutations in the KMT2A gene were observed exclusively in ULM and ULMS. In silico pathway analyses demonstrated that many genes mutated in ULMS and ESS have functions associated with the cellular response to hypoxia and cellular response to peptide hormone stimulus. In UCS and ADS, genes with most alterations have functions associated with phosphatidylinositol kinase activity and glycerophospholipid metabolic process.

CONCLUSION

This preliminary study observed pathogenic mutations in US and UCS samples. Further studies with a larger cohort and functional analyses will foster the development of a precision medicine-based approach for the treatment of US and UCS.

Uterine Tumor Resembling Ovarian Sex Cord Stromal Tumor (UTROSCT): A Series of 3 Cases With Extensive Rhabdoid Differentiation, Malignant Behavior, and ESR1-NCOA2 Fusions

ESR1 and GREB1 fusions have recently been described in uterine tumor resembling ovarian sex cord tumor (UTROSCT). Thus far, recurrences have been documented in a subset of those harboring GREB1 fusions, but not in those with ESR1 rearrangements. Here we describe the clinicopathologic features of 3 recurrent UTROSCTs with striking rhabdoid morphology (an unusual feature of these tumors overall) and ESR1-NCOA2 fusions. The patients were 32, 37, and 54 years at initial diagnosis and first recurrence occurred at 7, 9, and 32 years. The primary tumors (available in two cases) were centered in the myometrium and showed infiltrative borders. They predominantly grew in sheets and cords, but also had a pseudopapillary appearance. Cells were uniformly epithelioid with eccentric nuclei, prominent nucleoli, abundant eosinophilic globular/glassy (rhabdoid) cytoplasm, and infrequent mitoses (≤4/10 high-power fields [HPFs]). Recurrences were morphologically identical to the primary tumors, but demonstrated brisk mitotic activity (≥16/10 HPFs). The third tumor (with only recurrences available) had multiple patterns, including diffuse, corded, trabecular, and a focal retiform growth. Rhabdoid cells were conspicuous, but only comprised ~50% of the tumor, and mitoses numbered up to 2/10 HPFs. All tumors were strongly and diffusely positive for WT1, CAM5.2, ER, and PR, but negative for inhibin. Diffuse calretinin and desmin expression, as well as focal melan-A positivity, was noted in one tumor, but was negative in the others. In all 3 tumors, INI-1 and BRG-1 were retained, and ESR1-NCOA2 fusions were detected by targeted RNA sequencing. This study is the first to highlight an association between UTROSCTs with extensive rhabdoid differentiation, ESR1-NCOA2 fusions, and aggressive behavior. UTROSCTs are considered neoplasms of uncertain malignant potential, but have a benign course in most cases. Thus, it is important to be aware of these specific features and recommend long-term follow-up due to their propensity for late recurrences.

Update on SWI/SNF-related gynecologic mesenchymal neoplasms: SMARCA4-deficient uterine sarcoma and SMARCB1-deficient vulvar neoplasms

Our knowledge regarding the role of genes encoding the chromatin remodeling switch/sucrose non-fermenting (SWI/SNF) complex in the initiation and progression of gynecologic malignancies continues to evolve. This review focuses on gynecologic tumors in which the sole or primary genetic alteration is in SMARCA4 or SMARCB1, two members of the SWI/SNF chromatin remodeling complex. In this review, we present a brief overview of the classical example of such tumors, ovarian small cell carcinoma of hypercalcemic type, and then a detailed review and update of SMARCB1-deficient and SMARCA4-deficient tumors of the uterus and vulva.

Post-radiation Mullerian adenosarcoma with sarcomatous overgrowth: rare presentation of an uncommon malignancy

Mullerian adenosarcoma is an uncommon biphasic malignant uterine tumor. It is composed of benign epithelial and malignant stromal elements. We present a case of a 45-year-old woman who presented with post-menopausal bleeding for three months. She had a significant past medical history of pelvic irradiation for squamous carcinoma of cervix 20 years ago. Pathology revealed adenosarcoma with sarcomatous overgrowth. The patient had a recurrence of pure sarcoma three months later and unfortunately succumbed to her disease. The role of radiation in the pathogenesis of adenosarcoma has been uncommonly described compared to its well established role in the development of carcinosarcoma. Our case fulfils the criteria for a radiation induced sarcoma. We review the salient clinical and pathological features of this uncommon lesion highlighting the importance of sarcomatous overgrowth in these lesions and the possible role of radiation in the development of these tumors.

DICER1-associated embryonal rhabdomyosarcoma and adenosarcoma of the gynecologic tract: Pathology, molecular genetics, and indications for molecular testing

Gynecologic sarcomas are uncommon neoplasms, the majority occurring in the uterus. Due to the diverse nature of these, the description of "new" morphological types and the rarity of some of them, pathological diagnosis and treatment is often challenging. Finding genetic alterations specific to, and frequently occurring, in a certain type can aid in the diagnosis. DICER1 is a highly conserved ribonuclease crucial in the biogenesis of microRNAs and mutations in DICER1 (either somatic or germline) have been detected in a wide range of sarcomas including genitourinary embryonal rhabdomyosarcomas (ERMS) and adenosarcomas. Importantly, DICER1-associated sarcomas share morphological features irrespective of the site of origin such that the pathologist can strongly suspect a DICER1 association. A review of the literature shows that almost all gynecologic ERMS reported (outside of the vagina) harbor DICER1 alterations, while approximately 20% of adenosarcomas also do so. These two tumor types exhibit significant morphological overlap and DICER1 tumor testing may be helpful in distinguishing between them, because a negative result makes ERMS unlikely. Given that germline pathogenic DICER1 variants are frequent in uterine (corpus and cervix) ERMS and pathogenic germline variants in this gene cause a hereditary cancer predisposition syndrome (DICER1 syndrome), patients diagnosed with these neoplasms should be referred to medical genetic services. Cooperation between pathologists and geneticists is crucial and will help in improving the diagnosis and management of these uncommon sarcomas.

An update of molecular findings in uterine tumor resembling ovarian sex cord tumor and GREB1-rearranged uterine sarcoma with variable sex-cord differentiation

Uterine tumor resembling ovarian sex cord tumor (UTROSCT) is a uterine mesenchymal tumor defined histologically by showing sex cord-like growth patterns, such as sheets, nests, trabeculae, cords, or tubules, with/without Sertoli-like or Leydig-like components, and immunohistochemically by exhibiting variable sex cord markers in addition to epithelial, myogenic, and sex hormone markers. Recent years have seen the emergence in UTROSCT of novel fusion genes that involve key genes in sex hormone pathways, including ESR1 and GREB1 as the 5' partner, and (co)activator oncogenes, particularly NCOA1-3, as the 3' partner. While the identification of similar fusions in the majority of cases serves as a strong argument for UTROSCT to be a distinct entity, there is no denying significant clinicopathologic heterogeneity within the disease spectrum, which might to some extent correlate with the different fusion types. The current review gives a summary of the recently identified fusions in UTROSCT, along with their possible clinicopathologic relevance. Also discussed are unsolved issues including the relationship between UTROSCT and so-called GREB1-rearranged uterine sarcoma as well as other uterine mesenchymal tumors harboring similar fusions.

Recurrent DICER1 Hotspot Mutations in Malignant Thyroid Gland Teratomas: Molecular Characterization and Proposal for a Separate Classification

Thyroid gland teratomas are rare tumors that span a wide clinicopathologic spectrum. Although benign and immature teratomas arise in infants and young children and generally have good outcomes, malignant teratomas affect adults and follow an aggressive course. This divergent behavior raises the possibility that benign/immature and malignant teratomas are separate entities rather than different grades of a single tumor. However, the histogenesis and molecular underpinnings of thyroid gland teratomas are poorly understood regardless of grade. In this study, we performed next-generation sequencing on 8 thyroid gland teratomas, including 4 malignant, 3 benign, and 1 immature. We identified DICER1 hotspot mutations in all 4 malignant cases (100%) but not in any benign/immature cases (0%). No clinically significant mutations in other genes were found in either group. We also performed immunohistochemistry to characterize the primitive components of malignant teratomas. Not only did all cases consistently contain immature neural elements (synaptophysin and INSM1 positive), but also spindled cells with rhabdomyoblastic differentiation (desmin and myogenin positive) and bland epithelial proliferations of thyroid follicular origin (TTF-1 and PAX8 positive). Although DICER1 mutations have previously been implicated in multinodular hyperplasia and well-differentiated thyroid carcinomas, these findings demonstrate the first recurrent role for DICER1 in primitive thyroid tumors. The combined neural, rhabdomyoblastic, and homologous epithelial elements highlighted in this series of malignant thyroid gland teratomas parallel the components of DICER1-mutated tumors in other organs. Overall, these molecular findings further expand the differences between benign/immature teratomas and malignant teratomas, supporting the classification of these tumors as separate entities.

BCOR Expression in Mullerian Adenosarcoma: A Potential Diagnostic Pitfall

Adenosarcoma can mimic high-grade endometrial stromal sarcoma with ZC3H7B-BCOR fusion that may show entrapped glands and often exhibits diffuse BCOR expression. We encountered diffuse BCOR expression in rare adenosarcomas and sought to define its frequency among a larger cohort of these tumors. BCOR immunohistochemistry was performed on archival formalin-fixed paraffin-embedded tumor tissue in 13 of 14 adenosarcomas with and without stromal overgrowth arising in the uterus or ovary. The staining intensity and percentage of positive tumor nuclei in the mesenchymal component were evaluated. Eleven cases with sufficient tumoral tissue were subjected to fluorescence in situ hybridization for the detection of BCOR, BCORL1, NUTM1, ZC3H7B, and JAZF1 rearrangement. Three cases were subjected to targeted RNA sequencing. BCOR was expressed in 9 of 13 (70%) tumors, including 6 with and 3 without stromal overgrowth. Moderate to strong staining in >70% of cells was seen throughout in 1 low-grade and 6 high-grade tumors, 5 of which had stromal overgrowth. No staining was seen in 3 low-grade and 1 high-grade tumors with stromal overgrowth. One tumor demonstrating extensive sex cord-like differentiation and diffuse BCOR expression harbored JAZF1 and BCORL1 rearrangements. No BCOR or BCORL1 rearrangement was identified in the remaining tumors. BCOR expression is seen in most adenosarcomas with and without stromal overgrowth. BCORL1 rearrangement is seen in rare tumors with diffuse BCOR expression. Assessment of BCOR or BCORL1 rearrangement status is required in adenosarcomas demonstrating BCOR expression.

Pleuropulmonary blastoma-like peritoneal sarcoma: a newly described malignancy associated with biallelic DICER1 pathogenic variation

Since the original description of pathogenic germline DICER1 variation underlying pleuropulmonary blastoma (PPB), the spectrum of extrapulmonary neoplasms known to be associated with DICER1 has continued to expand and now includes tumors of the ovary, thyroid, kidney, eye, and brain among other sites. This report documents our experience with another manifestation: a primitive sarcoma that resembles PPB and DICER1-associated sarcoma of the kidney. These tumors are distinguished by their unusual location in the peritoneal cavity, associated with visceral and/or parietal mesothelium. A total of seven cases were identified through pathology review in children presenting at a median age of 13 years (range 3-14 years). Primary sites of origin included the fallopian tube (four cases), serosal surface of the colon (one case), and pelvic sidewall (two cases). One case had pathologic features of type I PPB, another type Ir (regressed) PPB, and the remaining five had features of type II or III PPB with a mixed primitive sarcomatous pattern with or without cystic elements. All had a pathogenic DICER1 variation identified in germline and/or tumor DNA. PPB-like peritoneal tumors represent a newly described manifestation of DICER1 pathogenic variation whose pathologic features are also recapitulated in DICER1-related renal sarcoma, cervical embryonal rhabdomyosarcoma, and some Sertoli-Leydig cell tumors with heterologous elements. Tumors arising from the fallopian tube or elsewhere in the abdomen/pelvis, especially those with heterogeneous rhabdomyosarcomatous and/or cartilaginous differentiation, should prompt consideration of germline and tumor DICER1 testing.

Pten and Dicer1 loss in the mouse uterus causes poorly differentiated endometrial adenocarcinoma

Endometrial cancer remains the most common gynecological malignancy in the United States. While the loss of the tumor suppressor, PTEN (phosphatase and tensin homolog), is well studied in endometrial cancer, recent studies suggest that DICER1, the endoribonuclease responsible for miRNA genesis, also plays a significant role in endometrial adenocarcinoma. Conditional uterine deletion of Dicer1 and Pten in mice resulted in poorly differentiated endometrial adenocarcinomas, which expressed Napsin A and HNF1B (hepatocyte nuclear factor 1 homeobox B), markers of clear-cell adenocarcinoma. Adenocarcinomas were hormone-independent. Treatment with progesterone did not mitigate poorly differentiated adenocarcinoma, nor did it affect adnexal metastasis. Transcriptomic analyses of DICER1 deleted uteri or Ishikawa cells revealed unique transcriptomic profiles and global miRNA downregulation. Computational integration of miRNA with mRNA targets revealed deregulated let-7 and miR-16 target genes, similar to published human DICER1-mutant endometrial cancers from TCGA (The Cancer Genome Atlas). Similar to human endometrial cancers, tumors exhibited dysregulation of ephrin-receptor signaling and transforming growth factor-beta signaling pathways. LIM kinase 2 (LIMK2), an essential molecule in p21 signal transduction, was significantly upregulated and represents a novel mechanism for hormone-independent pathogenesis of endometrial adenocarcinoma. This preclinical mouse model represents the first genetically engineered mouse model of poorly differentiated endometrial adenocarcinoma.

Gynecological Sarcomas: Molecular Characteristics, Behavior, and Histology-Driven Therapy

Gynecological sarcomas represent 3% to 4% of all gynecological malignancies and 13% of all sarcomas. The uterus is the most frequent primary site (83%); less frequently sarcomas are diagnosed originating from the ovary (8%), vulva and vagina (5%), and other gynecologic organs (2%). As the classification of gynecologic sarcomas continues to diversify, so does the management. Accurate histopathologic diagnosis, utilizing appropriate ancillary immunohistochemical and molecular analysis, could lead to a more personalized approach. However, there are subtypes that require further definition, with regard to putative predictive markers and optimal management. The aim of this review is to highlight the importance of accurate diagnosis and classification of gynecologic sarcoma subtypes by the surgical pathologist in order to provide more tailored systemic treatment, and to highlight the increasing importance of close collaboration between the pathologist and the oncologist.

Uterine mesenchymal tumours: recent advances

Almost all uterine mesenchymal tumours have been historically classified as either smooth muscle or endometrial stromal neoplasms. Recent application of molecular techniques has identified numerous lesions with distinctive genetic abnormalities and clinicopathological characteristics. Newly discovered uterine sarcoma subtypes include high-grade endometrial stromal sarcomas with BCOR genetic abnormalities, fibrosarcoma-like uterine sarcomas with NTRK rearrangements and COL1A-PDGFRB fusions, as well as undifferentiated uterine sarcomas with SMARCA4 mutations. Novel PLAG1 and PGR fusions have been identified in subsets of myxoid and epithelioid leiomyosarcomas. Some uterine tumours resembling ovarian sex-cord tumour harbour GREB1 and ESR1 rearrangements. Histological and immunophenotypical features as well as underlying genetic abnormalities defining these lesions are discussed.

Superior Vena Cava Syndrome associated with recurrent uterine adenosarcoma

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A woman with a history of Stage IA low-risk uterine adenosarcoma presented with shortness of breath and rib pain.

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She was found to have recurrent metastatic disease with resultant fatal SVC Syndrome.

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Better methods to determine which patients with uterine adenosarcoma are at risk of recurrence and death are needed.

NTRK fusion cervical sarcoma: a report of three cases, emphasising morphological and immunohistochemical distinction from other uterine sarcomas, including adenosarcoma

AIMS

A unique fibrosarcoma-like tumour of the uterine cervix harbouring a rearrangement of a neurotrophic tyrosine kinase receptor (NTRK) gene (NTRK1 or NTRK3) has recently been described in 11 young women, some with recurrence and/or metastasis. The aims of this study were to expand the morphological spectrum of this tumour by reporting three additional cases that showed adenosarcoma-like features not previously described, one of which is the first reported to respond to targeted therapy, and to evaluate 19 conventional uterine adenosarcomas for evidence of NTRK rearrangement.

METHODS AND RESULTS

Three patients presented with a polyp or mass confined to the cervix. The constellation of polypoid growth, spindle cell morphology, entrapped endocervical glands and intraglandular stromal projections raised diagnostic consideration for adenosarcoma with stromal overgrowth. Deep cervical wall invasion was present in two cases at hysterectomy, and the third was removed by polypectomy. All three stained for S100 and pan-Trk, but were negative for a spectrum of other diagnostic markers. All three harboured NTRK rearrangements (TPM3-NTRK1, TPR-NTRK1, and SPECC1L-NTRK3). One patient developed pleural metastases at 16 months, received the NTRK inhibitor larotrectinib, and is free of disease 15 months later. Two others are alive without disease. None of the uterine adenosarcomas showed any S100 or pan-Trk staining, or rearrangement of NTRK1, NTRK2 or NTRK3 on next-generation sequencing.

CONCLUSIONS

Unusual adenosarcoma-like spindle cell neoplasms of the cervix may represent an NTRK fusion sarcoma, which can be detected by S100 and pan-Trk staining and confirmed by NTRK molecular testing. Conventional uterine adenosarcomas do not harbour NTRK rearrangements.

Significantly greater prevalence of DICER1 alterations in uterine embryonal rhabdomyosarcoma compared to adenosarcoma

Embryonal rhabdomyosarcomas (ERMS) account for 2-3% of cancers in pediatric and adolescent populations. They are rarer in adults. We and others have reported that ERMS arising in the uterine cervix may harbor mutations in the gene encoding the microRNA biogenesis enzyme, DICER1, but a large series of cases has not been published. In the uterus, distinguishing ERMS from adenosarcoma can be very challenging, even for expert pathologists, and DICER1 alterations have been identified in a variable subset of uterine adenosarcomas. We hypothesized that DICER1 genetic testing may be useful in distinguishing between ERMS and adenosarcoma. We conducted a central pathology review-based study of 64 tumors initially thought to be uterine ERMS or adenosarcoma; 19 neoplasms had a consensus diagnosis of ERMS, 27 of adenosarcoma and for 18, no consensus diagnosis was reached. The median age at diagnosis was 30 years (range 2.5-69) for ERMS, 57.5 years (range 27-82) for adenosarcoma, and 65.5 years (range 32-86) for no consensus cases. In our series, the DICER1 mutation prevalence differed between the three groups: DICER1 alterations were present in 18/19 (95%) ERMS, 7/27 (26%) adenosarcomas (p < 0.001), and 4/18 (22%) no consensus cases. A germline alteration was present in 6/12 ERMS patients tested versus 0/6 adenosarcoma patients. Thus, although DICER1 mutations are near ubiquitous in uterine ERMS and are significantly less common in uterine adenosarcoma, DICER1 testing is only of value in distinguishing between the two neoplasms when a DICER1 mutation is absent, as this is helpful in excluding ERMS. On review of the clinical and radiological features of the single DICER1 wild-type cervical ERMS, this was thought most likely to be of vaginal origin. Given the significant prevalence of DICER1 germline pathogenic variants in uterine ERMS, all patients with this diagnosis should be referred to a genetics service.

DICER1 screening in 15 paediatric paratesticular sarcomas unveils an unusual DICER1-associated sarcoma

Individuals with DICER1 syndrome, a genetic disorder caused by pathogenic germline variants in DICER1, are at increased risk of developing a wide array of predominantly childhood onset conditions, including genitourinary sarcomas. However, data on DICER1 involvement in paratesticular sarcomas have not been published. Herein, we analyse a series of 15 paediatric paratesticular sarcomas and describe in detail the case of a male infant with a paratesticular myxoid tumour, considered to be a low‐grade sarcoma, who also manifested a cystic nephroma, a classic DICER1 syndrome phenotype. He harboured a pathogenic germline DICER1 variant and different somatic hot‐spot mutations in each tumour. The paratesticular tumour showed strong and diffuse expression for WT1 and CD10, an unusual immunophenotype in paediatric sarcomas, but typical of tumours of Müllerian origin. The tumour was postulated to arise from the appendix testis, a Müllerian remnant located in the paratestis. Such an origin would be analogous to other DICER1‐associated non‐epithelial gynaecological tumours, thought to arise from Müllerian derivatives. These findings point towards a key role of DICER1 in Müllerian‐derived structures. Supporting this hypothesis is the fact that the other paratesticular sarcomas from the series were either negative or focally positive for WT1 and for CD10, and none had any DICER1 mutations. In summary, we present the first case of a paratesticular sarcoma associated with DICER1 syndrome, emphasising that paratesticular tumours with an unusual histological appearance may suggest an underlying DICER1 mutation, especially in the presence of a personal or family history of DICER1‐associated disease. In this context, DICER1 mutation testing could lead to changes in clinical care including implementation of cancer care surveillance strategies.

Clinicopathologic Characterization of GREB1-rearranged Uterine Sarcomas With Variable Sex-Cord Differentiation

Uterine mesenchymal tumors are genetically heterogenous; those with uniform cytomorphology, best exemplified by endometrial stromal tumors, often contain various fusion genes. Novel fusions involving ESR1 and GREB1, key factors in sex hormone pathways, have been implicated in rare uterine mesenchymal tumors. Particularly, the fusions between 5'-ESR1/GREB1 and 3'-NCOA2/NCOA3 were recently identified in 4 uterine tumors resembling ovarian sex-cord tumor (UTROSCT). By RNA sequencing, pathology review, and FISH screening, we identified 4 uterine sarcomas harboring rearranged GREB1, including GREB1-NCOA2 and the novel GREB1-NR4A3, GREB1-SS18, and GREB1-NCOA1, validated by RT-PCR and/or FISH. They occurred in the myometrium of postmenopausal women and were pathologically similar despite minor differences. Tumor cells were generally uniform and epithelioid, with vesicular nuclei and distinct to prominent nucleoli. Growth patterns included solid sheets, trabeculae/cords, nests, and fascicles. Only 1 tumor showed small foci of definitive sex-cord components featuring well-formed tubules, retiform structures, Leydig-like cells, and lipid-laden cells and exhibiting convincing immunoreactivity to sex-cord markers (calretinin, α-inhibin, and Melan-A). In contrast, all the 4 classic UTROSCT we collected occurred in premenopausal patients, consisted predominantly of unequivocal sex-cord elements, prominently expressed multiple sex-cord markers, and harbored ESR1-NCOA3 fusion. Combined with previously reported cases, GREB1-rearranged tumors involved significantly older women (P=0.001), tended to be larger and more mitotically active, showed more variable and often inconspicuous sex-cord differentiation, and appeared to behave more aggressively than ESR1-rearranged UTROSCT. Therefore, these 2 groups of tumors might deserve separate consideration, despite some overlapping features and the possibility of belonging to the same disease spectrum.

Expanding the spectrum of dicer1-associated sarcomas

DICER1 syndrome is a hereditary cancer predisposition syndrome caused by deleterious germline DICER1 mutations. Characteristic "hotspot" somatic mutations of DICER1 have been identified in DICER1-associated tumors. With the exception of genitourinary embryonal rhabdomyosarcoma and anaplastic sarcoma of the kidney, sarcomas are rarely reported in DICER1 syndrome. Herein, we report the clinical, histopathologic, and molecular findings of a germline DICER1-associated ovarian sarcoma in a 5-year-old female, a somatic DICER1-associated metastatic peritoneal sarcoma in a 16-year-old female, and a somatic DICER1-associated primary intracranial sarcoma in a 4-year-old male. A comprehensive review of the literature, including 83 DICER1-associated sarcomas, illustrates an unequivocal histologic pattern mimicking pleuropulmonary blastoma, regardless of the site of origin. The features include undifferentiated small round blue cells, poorly differentiated spindle cells, and large bizarre pleomorphic cells (anaplasia), often with rhabdomyoblastic and/or chondroid differentiation, and rare bone/osteoid formation. This unique heterogeneous histologic pattern should raise suspicion for pathogenic DICER1 mutation(s) warranting a detailed review of the family history and DICER1 mutation analysis. In addition to expanding the phenotypic spectrum of DICER1-associated conditions, identification of pathogenic DICER1 variants facilitates optimized genetic counseling, caregiver education and judicious imaging-based surveillance.

Mutational and Immunophenotypic Profiling of a Series of 8 Tubo-ovarian Carcinosarcomas Revealed a Monoclonal Origin of the Disease

Carcinosarcomas are rare, highly aggressive neoplasms composed of a combination of carcinomatous and sarcomatous elements. These tumors represent a paradigmatic field for the study of intratumor heterogeneity. A series of 8 tubo-ovarian carcinosarcomas was characterized for the following: (i) immunohistochemical expression of MNF116, epithelial membrane antigen, vimentin, S100, chromogranin, synaptophysin, desmin, myogenin (MYF4), and p53; (ii) mutational profiling of KRAS, BRAF, PIK3CA, NRAS, TP53, and DICER1 genes. Heterologous differentiation was present in 6 of 8 tumors. Cytokeratin MNF116 and epithelial membrane antigen were positive in all the carcinomatous components and in 87.5% and 50.0% of the sarcomatous components, respectively. The sarcomatous components showed positive staining for vimentin in all cases. Two cases demonstrated positivity for neuroendocrine markers in their carcinomatous components. All rhabdomyosarcomas were positive for desmin and MYF-4. Chondrosarcomas were positive for S100. All but one tumor showed similar p53 immunoreactivity in both the carcinomatous and sarcomatous components, and one case showed cytoplasmic p53 expression. Three of 8 cases (37.5%) showed TP53 mutations, and, in 2 cases, the TP53 mutation was shared by both epithelial and mesenchymal components. DICER1 mutation was found in all components of one case. Mutations in KRAS, NRAS, BRAF, and PIK3CA genes were not found in the study cohort. Our results highlight the heterogeneity of ovarian carcinosarcomas at the phenotypic level. A common mutational signature was observed in both components in 3 of 4 informative tumors. More studies are required to dissect different levels of ovarian carcinosarcomas' heterogeneity in order to define the best therapeutic approaches to these aggressive neoplasms.

Two cases of primary supratentorial intracranial rhabdomyosarcoma with DICER1 mutation which may belong to a "spindle cell sarcoma with rhabdomyosarcoma-like feature, DICER1 mutant"

Rhabdomyosarcoma is the most common soft-tissue sarcoma affecting children and adolescents. It is defined as a malignant neoplasm characterized by morphologic, immunohistochemical, ultrastructural, or molecular genetic evidence of primary skeletal muscle differentiation, usually in the absence of any other pattern of differentiation. Primary intracranial rhabdomyosarcoma (PIRMS) is an extremely rare neoplasm, with only 60 cases reported in the literature, and generally has poor prognosis with an overall survival of only 9.1 months. The DICER1 gene encodes an RNA endoribonuclease that plays a key role in gene expression regulation through the production of small RNAs. Herein, we report two cases of PIRMS with somatic DICER1 mutation showing morphological and immunohistochemical evidence of primary skeletal muscle differentiation; the two cases share common clinical features, including young age, supratentorial tumor, and onset of intratumoral bleeding. Although methylation profiling was not performed, both cases shared clinical and pathological characteristics in common with recently proposed methylation entity "spindle cell sarcoma with rhabdomyosarcoma-like features, DICER1 mutant (SCS-RMSlike-DICER1)''. Our cases provide further evidence of the link between primary intracranial sarcoma and DICER1 mutation which may form a distinct entity.

PRRX-NCOA1/2 rearrangement characterizes a distinctive fibroblastic neoplasm

Fibroblastic/myofibroblastic neoplasms represent a broad, and occasionally diagnostically challenging, category of soft tissue neoplasms. A subset of these tumors defy conventional classification. However, with the advent of next-generation sequencing, the identification of disease-defining molecular alterations is gradually improving their subclassification. Following identification of two index cases of a distinctive fibroblastic neoplasm with a fusion gene involving PRRX1 and NCOA1, we performed a retrospective review to further characterize this entity. We identified two additional cases, including one with a fusion between PRRX1 and NCOA2. The average patient age was 38 years, and three patients were female. Two tumors occurred on the neck, and the others involved the groin and thigh. Tumors were centered in the subcutis and ranged from 2.3 to 14.0 cm (average 5.8 cm). Morphologically, they were predominantly hypocellular, with focal hypercellularity. They were composed of monomorphic spindle-stellate cells with a vague fascicular pattern. The nuclei were bland with only rare mitotic activity, and occasional multinucleation. The intervening stroma was typically abundant and ranged from myxoid to collagenous, with frequent rope-like collagen bundles. Three of the cases had a prominent vasculature ranging from numerous small curvilinear vessels to ectatic and branching staghorn-like vessels. Immunohistochemistry was negative for desmin, smooth muscle actin, S100, CD34, keratin, and epithelial membrane antigen. Each of the patients was treated by simple excision and none of the tumors were associated with local recurrence or metastasis. Based on their unique morphological and molecular attributes, we believe this represents a novel fibroblastic tumor for which we have tentatively proposed the name "PRRX-NCOAx-rearranged fibroblastic tumor."