Primary adenosquamous carcinoma of the jejunum.

Adenosquamous carcinomas of the small intestine are extremely rare, with only three documented jejunal and three ileal cases being reported in the English-language medical literature. Presented herein is a case of primary jejunal adenosquamous carcinoma in an 80-year-old woman. The jejunal carcinoma consisted predominantly of a squamous component throughout the tumor but peritoneal nodules carrying metastases from the adenocarcinoma element were noted, making it the first case of jejunal adenosquamous carcinoma with metastases from the adenocarcinoma component. The finding that metastases could arise from the minor component of a jejunal adenosquamous carcinoma indicates that an accurate diagnosis must be based upon thorough examination of both the primary and the metastases, not just mesenteric nodule biopsy alone. Histological foci of closely intermingled squamous and glandular components with apparent morphological transition were noted, indicating the pathogenetic possibility that the squamous component might arise by transformation from the glandular element. The squamous component was strongly positive with immunostaining for p63 (nuclear staining) and for cytokeratin 10/13 (cytoplasmic staining), while the adenocarcinoma element was negative. The immunohistochemical results suggest that p63 and cytokeratin 10/13 might be useful in identifying squamous differentiation in jejunal carcinoma.