Mucinous carcinoma originating in the peritoneum diagnosed by an ascites cell block: a case report

BACKGROUND: Peritoneal carcinoma is a rare disease that is diagnosed and treated in a manner similar to ovarian cancer. In most cases, the histological type is serous carcinoma, and chemotherapy is effective. However, there are a few case reports of mucinous peritoneal carcinoma. We inferred the histological type before surgery using an ascites cell block sample, which was useful for determining the treatment plan. CASE PRESENTATION: Our patient was a 60-year-old Japanese woman. She presented with a feeling of fullness in the abdomen. A computed tomographic scan showed a large quantity of ascitic fluid and thickening of the greater omentum, as well as thickening of the peritoneum at the pouch of Douglas and diaphragm. Hence, peritoneal carcinoma was suspected. The tumor markers carcinoembryonic antigen, cancer antigen 19-9, and cancer antigen 125 were all increased, and no malignant findings were observed in the uterus or ovaries. Cells suggestive of carcinoma were found in the ascitic fluid, and immunostaining by the cell block method suggested the possibility of mucinous carcinoma. The preoperative chemotherapy strategy was changed to short courses, and tumor reduction surgery was planned. Similar to the suspicion before surgery, the pathology results indicated mucinous carcinoma, and the therapeutic effect of chemotherapy was grade 0. CONCLUSIONS: Determining whether peritoneal carcinoma is serous carcinoma is important for therapy and prognostic prediction. In this case, we encountered a patient for whom surgery was chosen because of drug therapy resistance inferred through histological type estimation using the cell block method. Inferring the histological type by cell block preparation is useful for diagnosis and treatment selection.