Microscopic Primary Tubal Serous Carcinoma With Colon Metastasis and Paraneoplastic Neurological Syndrome: A Case Report

This case report discusses a rare instance of a 69‐year‐old woman presenting with lower limb paresthesia, whose imaging showed suspicious nodules in the sigmoid colon and no other obvious sites of malignancy. Laparoscopic anterior resection was performed and subsequent immunohistochemical examination revealed an unexpected diagnosis of colonic metastasis from a carcinoma of tubo‐ovarian origin, which necessitated a second surgery. Metastatic lesions of the colon from other organs are uncommon, and accurate diagnosis without clear evidence of the primary tumor poses a challenge. This case emphasizes the consideration for re‐biopsy when initial samples lack sufficient tissue for thorough immunohistochemical examination, highlighting the importance of detailed histopathology in guiding diagnosis and treatment in metastatic cases. We also discuss the utility of identifying paraneoplastic neurological syndromes and onconeural antibodies in determining the tubo‐ovarian origin of cancer.