RESUMO
BACKGROUND: Colorectal cancer is the third most commonly diagnosed cancer in both men and women, and one of the more widely recognized preventable cancers. Adenosquamous carcinoma (ASC) of the colon/rectum is an uncommon disease that consists of both glandular and squamous components, and the most common site of ACS is the right and transverse colon. CASE REPORT: Here, we present the case of a 78-year-old woman, who complained of abdominal pain. Colonoscopy revealed a circumscribed tumor in the ascending colon, and no specific lesion was detected in the other areas of the colon or rectum. ASC (pT3N0M0) was diagnosed from right hemicolectomy specimens. Three months after the first surgery, the serum levels of tumor markers had gradually increased, and a new tumor was subsequently detected in the sigmoid colon 2 months later. The sigmoid lesion was surgically resected and diagnosed as ASC (pT3N3M0). Strong PD-L1 expression was also found in the squamous component. CONCLUSION: To our knowledge, this is the first report of a recurrent sigmoid colon ASC that likely originated from the ascending colon, and PD-L1/PD-1 signaling was likely involved in the immune escape mechanism.