Dedifferentiated endometrial carcinoma is an aggressive type of endometrial cancer that contains a mix of low-grade endometrioid and undifferentiated carcinoma components. We performed targeted sequencing of eight dedifferentiated carcinomas and identified somatic frameshift/nonsense mutations in SMARCA4, a core ATPase of the switch/sucrose non-fermenting (SWI/SNF) complex, in the undifferentiated components of four tumors. Immunohistochemical analysis confirmed the loss of SMARCA4 in the undifferentiated component of these four SMARCA4-mutated cases, whereas the corresponding low-grade endometrioid component showed retained SMARCA4 expression. An expanded survey of other members of the SWI/SNF complex showed SMARCB1 loss in the undifferentiated component of two SMARCA4-intact tumors, and all SMARCA4- or SMARCB1-deficient tumors showed concomitant loss of expression of SMARCA2. We subsequently examined the expression of SMARCA2, SMARCA4, and SMARCB1 in an additional set of 22 centrally reviewed dedifferentiated carcinomas and 31 grade 3 endometrioid carcinomas. Combining the results from the index and the expansion set, 15 of 30 (50%) of the dedifferentiated carcinomas examined showed either concurrent SMARCA4 and SMARCA2 loss (37%) or concurrent SMARCB1 and SMARCA2 loss (13%) in the undifferentiated component. The loss of SMARCA4 or SMARCB1 was mutually exclusive. All 31 grade 3 endometrioid carcinomas showed intact expression of these core SWI/SNF proteins. The majority (73%) of the SMARCA4/SMARCA2-deficient and half of SMARCB1/SMARCA2-deficient undifferentiated component developed in a mismatch repair-deficient molecular context. The observed spatial association between SWI/SNF protein loss and histologic dedifferentiation suggests that inactivation of these core SWI/SNF proteins may contribute to the development of dedifferentiated endometrial carcinoma.

Endometrioid, serous, and clear cell carcinomas are the major types of endometrial carcinoma. Histologic distinction between these different tumor types can be difficult in high-grade cases, in which significant interobserver diagnostic disagreement exists. Endometrioid and clear cell carcinomas frequently harbor ARID1A and/or PTEN mutations. Serous carcinoma acquires TP53 mutations/inactivation at onset, with a significant subset harboring an additional mutation in PPP2R1A. This study examines the correlation between tumor histotype and genotype in 36 previously genotyped high-grade endometrial carcinomas. This included 23 endometrioid/clear cell genotype and 13 serous genotype tumors. Eight subspecialty pathologists reviewed representative online slides and rendered diagnoses before and after receiving p53, p16, and estrogen receptor immunostaining results. κ statistics for histotype-genotype concordance were calculated. The average κ values for histotype-genotype concordance was 0.55 (range, 0.30 to 0.67) on the basis of morphologic evaluation alone and it improved to 0.68 (range, 0.54 to 0.81) after immunophenotype consideration (P<0.001). Genotype-incompatible diagnoses were rendered by at least 2 pathologists in 12 of 36 cases (33%) (3 cases by 2/8 pathologists, 2 by 3/8, 2 by 4/8, 3 by 6/8, 1 by 7/8, and 1 case by 8/8 pathologists). Six of the 12 were endometrioid/clear cell genotype tumors, and the other 6 were serous genotype tumors. The histopathologic features associated with histotype-genotype–discordant cases were reviewed, and specific diagnostic recommendations were made to improve concordance. This study found that although the majority of morphologic diagnoses are genotype concordant, genotype-incompatible diagnoses are made in a significant subset of cases. Judicious use and interpretation of p53 immunohistochemistry in selected scenarios can improve histotype-genotype concordance.

Dedifferentiated carcinoma of the endometrium or the ovary is an aggressive epithelial malignancy that comprises an endometrioid carcinoma together with an undifferentiated carcinoma. We recently reported that inactivation of BRG1 or INI1, core subunits of the switch/sucrose non-fermenting (SWI/SNF) complex, was the likely molecular event underlying dedifferentiation in about half of dedifferentiated carcinomas. In this study, we performed a genomic screen that included other members of the SWI/SNF complex to better delineate the molecular basis in the remainder of these tumours. We identified concurrent inactivating mutations involving ARID1A and ARID1B in 12 of 24 BRG1/INI1-intact, 0 of 3 INI1-deficient and 0 of 16 BRG1-deficient dedifferentiated carcinomas. All ARID1A and ARID1B co-mutated tumours displayed loss of ARID1A expression in the undifferentiated component with 11 of 12 tumours also displaying absent staining in the endometrioid component. ARID1B expression was absent in the undifferentiated component in all 12 tumours, whereas the corresponding endometrioid component showed intact expression. Clinically, ARID1A/ARID1B co-inactivated tumours showed similar aggressive behaviour to BRG1 or INI1-inactivated tumours. Given that ARID1A and ARID1B are the only known DNA-binding subunits of the SWI/SNF-A complex, additional inactivation of ARID1B in an ARID1A-deficient background appears to represent an alternative mechanism of disruption of SWI/SNF-mediated transcriptional regulation, resulting in arrested cellular differentiation in endometrial and ovarian endometrioid cancer.

Uterine carcinosarcoma is a clinically aggressive malignancy composed of a mix of carcinomatous and sarcomatous elements. We performed targeted next‐generation sequencing of 27 uterine cancer and sarcoma genes together with immunohistochemical analyses of selected proteins in 30 uterine carcinosarcomas. This included 13 cases in which the distinct carcinoma and sarcoma components were sequenced separately and 10 cases where the metastatic tumours were analysed in addition to the primary tumours. We identified non‐synonymous somatic mutations in 90% of the cases, with 27 of 30 cases (90%) harbouring TP53 alterations. The PI3K pathway was the most commonly mutated signalling pathway with mutations identified in PIK3CA, PTEN, PIK3R1, and/or PIK3R2 in two‐thirds of the cases. Mutations in FBXW7, PPP2R1A, ARID1A and KRAS were demonstrated in a minority of cases. In cases where the carcinomatous and sarcomatous components were separately analysed, most of the mutations identified were present in both components, indicating a common origin for the two components. Furthermore, the same TP53 alterations and/or PI3K pathway mutations seen in the primary tumours were also identified in the metastatic sites. Overall, carcinosarcomas exhibited heterogeneous molecular features that resemble the heterogeneity seen in endometrial carcinomas, with some showing endometrioid carcinoma‐like and others showing serous carcinoma‐like mutation profiles. While patients with serous‐like tumours presented more frequently with advanced‐stage disease compared to patients with endometrioid‐like tumours, there was no statistical difference in outcome between the two groups. Our results provide insights into the oncogenesis of uterine carcinosarcoma and identify targetable mutations that represent early oncogenic events. The findings of the different molecular types of uterine carcinosarcoma that parallel the different molecular types in endometrial carcinoma may have future treatment implications with targeted therapies.

Undifferentiated endometrial carcinoma is an aggressive type of endometrial carcinoma that typically presents with advanced stage disease and rapid clinical progression. In contrast to dedifferentiated endometrial carcinoma, undifferentiated carcinoma lacks a concurrent differentiated (typically low-grade endometrioid) carcinoma component, though the undifferentiated component of dedifferentiated carcinoma is similar histologically and immunophenotypically to pure undifferentiated carcinoma. We recently identified 3 mutually exclusive mechanisms of switch/sucrose nonfermentable (SWI/SNF) complex inactivation (BRG1 inactivation, INI1 inactivation or ARID1A/ARID1B co-inactivation) that are associated with histologic dedifferentiation in the majority of dedifferentiated endometrial carcinoma. In the current study, we aimed to determine by immunohistochemistry whether these patterns of SWI/SNF inactivation also occur in undifferentiated endometrial carcinomas. Of the 34 undifferentiated carcinomas examined, 17 (50%) exhibited SWI/SNF complex inactivation, with 11 tumors showing complete loss of both ARID1A and ARID1B, 5 showing complete loss of BRG1 and 1 showing complete loss of INI1. Ten of the remaining 17 undifferentiated carcinomas showed the following alterations: 5 tumors (15%) showed loss of ARID1A only with intact ARID1B, BRG1, and INI1 expression, 4 tumors (12%) showed mutated patterns of p53 staining with intact SWI/SNF protein expression, and 1 tumor (3%) harbored a POLE exonuclease domain mutation (P286R). SWI/SNF complex-inactivated tumors presented more frequently with extrauterine disease spread than those with intact expression (88% vs. 41%, respectively). In addition, patients with SWI/SNF complex-inactivated tumors had a significantly worse disease-specific survival (P=0.02). The findings here demonstrate frequent SWI/SNF complex inactivation in undifferentiated endometrial carcinomas, which has future implications regarding therapies that target chromatin remodelling and epigenetic control.