Metastatic signet ring cell carcinoma of unknown primary origin: a case report and review of the literature

In spite of the increasingly sophisticated diagnostic workup, detailed investigations fail to reveal a primary site of origin for about 3–5% of metastatic tumors. The most commonly reported subtype in cancer of unknown primary origin is adenocarcinoma. Signet ring cell carcinoma (SRCC) is a rare poorly differentiated aggressive subtype of adenocarcinoma that most commonly arise from the gastrointestinal tract. It usually presents late and is associated with poor prognosis. Treatment options remain limited to anecdotal reports. However, immunohistochemical studies can be useful in suggesting an origin and therefore may help guide investigations and treatment options. Here we present an unusual case of metastatic SRCC of unknown primary origin presenting as peritoneal carcinomatosis in a 73-year-old man. We also review the literature on metastatic SRCC of unknown primary origin and discuss the relevant findings. This work highlights the importance of collaboration between clinicians and pathologists as well as detailed histopathological, immunohistochemical, and molecular analyses which can help guide investigations and management options.