Primary signet ring cell carcinoma of the colon masquerading as foamy histiocytic collections on preoperative biopsy

Primary signet-ring cell carcinoma (PSRCC) is a rare pathological subtype of colorectal cancer, characterized by the presence of malignant signet ring cells. We report the case of PSRCC in an elderly female who was misdiagnosed on preoperative biopsy. PSRCC is usually diagnosed in young adults; the most common site is the ascending colon. It is clinically aggressive and has a poor prognosis. The distinctive signet ring cells, however, can often be misinterpreted as other benign cells: the so-called “benign signet-ring change.” Accurate and timely diagnosis of signet ring cell carcinoma is important because of its aggressive clinical course. Distinction from benign entities requires clinical and radiological correlation as well as a proper morphological assessment in conjunction with immunohistochemistry evaluation.