Clear Cell Carcinoma of the Left Colon: A Case Report.

BACKGROUND Primary clear cell carcinoma of the colon is an exceptionally rare condition. It is still uncertain whether this carcinoma represents a separate biological category or simply a variant of typical colorectal cancer. From a diagnostic standpoint, the presence of clear cell morphology introduces significant challenges, as similar features can be observed in various other carcinomas, including renal, ovarian, and endometrial carcinoma. Typically, primary colorectal tumors demonstrate positivity for markers such as CK20 and CDX2, supporting intestinal origin. CASE REPORT We present a case of primary clear cell carcinoma of the sigmoid colon, with no adenoma component, in a 69-year-old woman. The tumor was detected on routine bowel screening colonoscopy, and the patient underwent anterior resection of a pT3N2b sigmoid tumor with prophylactic oophorectomy and salpingectomy. In contrast to the positivity for intestinal-origin markers typically seen in primary colorectal tumors, in this case, the histopathological and immunohistochemical analyses revealed that the tumor was positive for AMACR, CK7, and PAX 8 and negative for WT1, ER, PR, P16, CD10, CDX2, and CK20. These results were consistent with colonic clear cell carcinoma. CONCLUSIONS Specific data on colorectal clear cell carcinoma in Ireland and worldwide are limited. In academic literature, few cases have been documented. The presence of clear cell morphology in colon tumors presents significant diagnostic challenges, necessitating careful radiological and histopathological evaluation, which should be correlated with the patient's clinical history. This case was documented due to the extreme rarity of this condition and the diagnostic difficulties it poses, particularly in distinguishing clear cell carcinoma of the colon from conventional adenocarcinoma.