Adenosquamous carcinoma of the right colon with diffuse signet-ring mucinous component.

Colorectal carcinoma is one of the most frequent human malignant neoplasms. Besides the most common histological types, colorectal adenosquamous carcinoma is very rare, being microscopically constituted by tumoural glandular and squamous components. The diagnosis of primary colon adenosquamous carcinoma requires the exclusion of a metastatic squamous cell carcinoma and the extension of a primary squamous cell carcinoma from the anal-rectum junction. We report a case of primary adenosquamous carcinoma of the ascending colon in a 62-year-old Caucasian man affected by long-standing ulcerative colitis. Peritumoural lymph nodes and distant metastasis were present. We reported also a diffuse signet-ring mucinous component, which has not been previously observed. Moreover, we investigated microsatellite and all-RAS/B-RAF status, p16 and p53 protein expression, and the molecular presence of human papillomavirus DNA in all the morphologically distinct components, in order to suggest pathogenetic factors influencing the aggressive prognosis of colon adenosquamous carcinoma.