RESUMEN
A 61-year-old woman was hospitalized with a 5-week history of abdominal discomfort, change in bowel habits, and weight loss. Colonoscopy showed a protruded tumor of the sigmoid colon first diagnosed as undifferentiated carcinoma. Surgical resection of the sigmoid colon was performed. Histological examination of the surgical specimen showed a proliferation of basaloid cells arranged in tumor clusters with central comedonecrosis and peripheral palisading of the nuclei. The tumor invaded the subserosa and presented liver metastasis without lymph node metastases. The tumor cells were marked by keratin AE1/AE3, keratin 5/6, epithelial membrane antigen, bcl-2, vascular endothelial growth factor, CD105, neuron-specific enolase, MLH-1, MSH-2, and p53, and were negative for keratin 7/20, chromogranin, synaptophysin, carcinoembryonic antigen, p63, c-KIT, and maspin. A high p53 nuclear index was also detected. On the basis of these characteristics and molecular examinations, the final diagnosis was microsatellite stable/human papilloma virus-negative/K-ras mutated/BRAF wild-type basaloid carcinoma (BC). Only seven BCs of the colon were reported in the literature, this being the eighth one and the first case that reports new molecular findings about microsatellite instability, K-ras/BRAF mutations, angiogenesis, and maspin expression in BC, with direct involvement in targeted therapy.