Primary Squamous Cell Carcinoma of the Colon With Peritoneal Carcinomatosis: A Case Report and Literature Review

Background: Primary squamous cell carcinoma (SCC) of the colon is an exceedingly rare malignancy, accounting for only 0.1–0.25 per 1,000 colorectal cancers. Its etiology remains unclear, with proposed mechanisms including chronic inflammation, infection, prior radiation, or squamous metaplasia in a pre-existing adenoma. Due to its rarity, optimal management is not well defined and prognosis is often poor. We present a case of a young female patient with primary colonic SCC that rapidly metastasized, and we review the relevant literature. Case Presentation: A 38-year-old woman with no significant medical history presented with acute large bowel obstruction. An emergency right hemicolectomy was performed, and pathology revealed a poorly differentiated squamous cell carcinoma of the ascending colon. No glandular (adenocarcinomatous) component was identified. Immunohistochemistry showed tumor cells positive for p40, confirming squamous phenotype, and negative for cytokeratin (CK)7, CK20, CD56, GATA3, and synaptophysin, helping to exclude other carcinoma types. Extensive evaluation found no other primary tumor, establishing this as a primary colonic SCC. Postoperatively, a restaging CT scan at 6 weeks showed extensive peritoneal carcinomatosis. The patient received three cycles of palliative combination chemotherapy with 5-fluorouracil and cisplatin. Despite treatment, the disease progressed on imaging at three months. The patient’s condition deteriorated, and she died five months after surgery. Conclusion: Primary SCC of the colon is a rare and aggressive disease. This case highlights the importance of thorough diagnostic evaluation to confirm the colonic origin and the challenges in management due to rapid metastatic progression. There is no established treatment protocol; surgery is typically the mainstay, while the benefits of chemotherapy or radiation remain uncertain. The prognosis of colonic SCC is significantly worse than that of conventional colon adenocarcinoma, especially in advanced stages. Further reports and research are needed to guide therapy for this unusual colorectal malignancy.