Synchronous serrated adenoma of the appendix and high-grade ovarian carcinoma: a case demonstrating different origin of the two neoplasms.

Association of mucinous adenomas of the appendix and mucinous ovarian tumors is well known. The origin of the ovarian tumor (metastasis from the appendix vs independent primary) is still debated. Serrated adenoma is a rare neoplasm of the distal gastrointestinal tract, and its precancerous role in the colorectum was recently postulated. A 74-year-old patient was subjected to hysterectomy with routine appendectomy due to a 17-cm tumor of her right ovary. Histological examination revealed a high-grade ovarian adenocarcinoma with peritoneal involvement. The appendix, grossly unremarkable, harbored a serrated adenoma with no evidence of invasion or malignant transformation. Immunohistochemical examination revealed CD7+, CK20-phenotype of the ovarian and reverse (CK7-, CK20+) phenotype of the appendiceal tumor. Microsatellite analysis demonstrated microsatellite instability (MSI-high) within the serrated adenoma (4/5 markers with positive amplification) and no MSI (0/6 amplified markers) in the samples from the ovarian carcinoma, its metastases and the uninvolved uterine cervix. There were also differences in LOH pattern between the ovarian adenocarcinoma and the serrated adenoma. The findings suggest two independent primaries with profound differences in tumorigenetic pathways of both lesions. To the best of our knowledge this is the first report of synchronous serrated adenoma of the appendix and ovarian carcinoma.