SWI/SNF chromatin-modification complexes use the energy of ATP hydrolysis to remodel nucleosomes and to affect transcription and several cellular processes. Accordingly, their loss of function has been associated with malignant transformation. ARID1A (the expression of whose product, BAF250a, a key complex component, is lost when mutated) has recently been identified as a tumor suppressor gene that is mutated in 46-57% of ovarian clear cell carcinoma (CCC). The purposes of this study are to assess the frequency of loss of BAF250a expression in endometrial CCC and whether this loss has any discernable clinicopathologic implications. 34 endometrial carcinomas with a CCC component (including 22 pure CCC, 8 mixed carcinomas with a 10% CCC component, and 4 carcinosarcomas with a CCC epithelial component), were evaluated by immunohistochemistry using a monoclonal antibody directed against the human BAF250a protein. 5 (22.7%) of the 22 pure CCC were entirely BAF250a negative, whereas the remainder showed diffuse immunoreactivity. None of 4 carcinosarcomas and only 1 (12.5%) of the 8 mixed carcinomas were BAF250a negative. There was no discernable relationship between BAF250a immunoreactivity status and tumor architectural patterns (solid, papillary or tubulocystic areas) or cell type (flat, hobnail or polygonal). Of the 22 patients with pure CCC, 14, 2, 3, and 3 were International Federation of Gynecology and Obstetrics stages 1, II, III and IV respectively. Interestingly, all 5 BAF250a negative cases were late stage [stages III or IV] as compared with 1 of 17 BAF250a positive cases (p=0.0002). Thus, 83% (5/6) of all late stage cases were BAF250a [-], as compared with 0 (0%) of the 16 early stage (I or II) cases (p=.0002). BAF250a negative and positive cases did not show any statistically significant difference regarding patient age and frequency of lymphovascular invasion or myometrial invasion. As may be anticipated from the concentration of late stage cases in the BAF250a negative group, patient outcomes were worsened in that group on univariate analysis. In conclusion, we found in this pilot assessment that 22.7% of endometrial CCC displays complete loss of BAF250a expression. There was a disproportionate concentration of BAF250a negative cases in the late stage group, with the attendant possibility of an associated worsened prognosis for those CCC patients whose tumors are BAF250a negative. These preliminary findings suggest the need for larger analyses to evaluate the prognostic significance, if any, of the loss of BAF250a expression in this rare histotype of endometrial cancer.
Keywords: ARID1A; BAF250a; endometrial cancer.