Rectal adenocarcinoma with a yolk sac tumor component: A rare case report and review of the literature

Yolk sac tumor (YST) occurs primarily in the gonads but rarely outside the gonads. They typically arise in the midline location, and there are only a few reports describing the colon and rectum as the primary sites of YST. Additionally, colorectal cancers containing YST-like components are rare, and in other organs, including the stomach, it is more common to describe such lesions as " yolk sac tumor-like carcinoma". Here, we report a case of colorectal adenocarcinoma with a YST-like component arising in the rectum. This is the seventh reported case of colorectal YST-like carcinoma. A 66-year-old man presented to our hospital with the chief complaint of anal bleeding. Colonoscopy revealed a 25 × 20 mm tumor located 5 cm above the anal verge. Biopsy results showed moderately differentiated tubular adenocarcinoma, cT3, cN2b, cM0, and cStage IIIC (UICC 8th edition). Subsequently, a laparoscopic abdominoperineal resection was performed. A histopathological examination of the resected specimen revealed findings of adenocarcinoma and YST-like component. Immunostaining for mismatch repair proteins revealed no abnormalities. The tumor was positive for the <i>KRAS</i> G12S mutation, and negative for the <i>BRAF</i> mutation. The overall diagnosis was adenocarcinoma with a YST-like component, pT3, pN2a, cM0, and pStage IIIB (UICC 8th edition). Six months after the surgery, metastasis was found in the liver, but at the request of the patient and their family, the decision was made not to undergo any aggressive treatment. We describe the clinical and pathological features of colorectal YST-like carcinoma that aid in its accurate diagnosis and provide treatment suggestions.