Abstract
Background : Endometrioid adenocarcinoma is relatively rare, compared with serous adenocarcinoma, in peritoneal washing cytology. We report herein on a case where identification of endometrioid adenocarcinoma cells in peritoneal washing cytology was difficult.
Case : The patient was a woman in her 50’s. She was histologically diagnosed as having an endometrioid adenocarcinoma from a biopsy, and a simple hysterectomy, bilateral salpingo-oophorectomy and peritoneal washing cytology were performed. The peritoneal washing cytology revealed tumor cells with prominent nucleoli which appeared as isolated cells or small clusters, and those cells were larger than normal mesothelial cells. Tumor cells also showed window-like formations which are seen in reactive mesothelial cells. Although the nuclear atypia of the cancer cells was slight, these findings led us to suspect malignancy. Therefore, we performed immunostaining to determine whether these cells were cancer cells. The immunocytochemistry findings showed tumor cells which expressed EMA and ERA (MOC-31), but not calretinin. We made a diagnosis of adenocarcinoma. On histological sections, the tumor showed tubular and solid growth patterns with central necrosis, and a focally squamous differentiation component. Individual tumor cells often had a pleomorphic nucleus or mitotic figures. Based on these findings, the patient was diagnosed as having endometrioid adenocarcinoma, grade 3 with squamous differentiation of the uterus body.
Conclusions : When cancer cells with weak atypia show a pseudo-window similar to the window formation of reactive mesothelium cells in effusion cytology, distinguishing between mesothelial cells and cancer cells is difficult. In such cases, we should use immunostaining to avoid a missed diagnosis.
