The diagnostic role of PTEN and ARID1A in serous effusions

The aim of this study was to analyze the diagnostic role of PTEN and ARID1A in effusion cytology. Effusions (n = 279), consisting of 226 carcinomas (70 ovarian, 64 breast, 36 lung, and 15 uterine corpus carcinomas; 41 carcinomas of other origin) and 53 malignant mesotheliomas, were analyzed for PTEN and ARID1A expression using immunohistochemistry. PTEN was preserved in 166 (59%) tumors, partially lost in 38 (14%), and absent in 75 (27%), with lower expression in malignant mesotheliomas compared to carcinomas, though not significantly (p = 0.084). ARID1A was preserved in 243 (88%) tumors, partially lost in 18 (6%), and absent in 18 (6%). The majority of tumors with absent ARID1A were ovarian carcinomas, predominantly of clear cell or low-grade serous type. Reactive mesothelial cells in carcinoma specimens were uniformly positive for both proteins. ARID1A mutation analysis showed no mutations in eight analyzed specimens negative by immunohistochemistry. Loss of PTEN and ARID1A expression is highly specific for malignancy in effusion pathology. Loss of PTEN is not informative of organ of origin, whereas absence of ARID1A should raise suspicion of an ovarian primary.