Adenosquamous carcinoma is a rare histologic subtype of extrahepatic bile duct (EBD) carcinoma and limited information is available on its clinicopathologic characteristics. Twelve cases of adenosquamous carcinoma were collected from 3 institutions and their clinicopathologic characteristics were examined and compared with those of 176 EBD adenocarcinomas. The adenocarcinoma component was more often seen at the surface of the tumor (7 of 12 cases, 58%), while the squamous carcinoma component was slightly more frequent at the advanced edge (7 of 12 cases, 58%). Immunohistochemistry, available in 10 cases, revealed that S100A2 was positive in the squamous carcinoma component in all 10 cases (100%), while it was present in the adenocarcinoma component in only 2 of 10 cases (20%, chi-square test, p=0.001). S100A4 expression did not show any difference between the two components. Patients with adenosquamous carcinomas had worse survival (median survival, 11 months) than those with adenocarcinoma (median survival, 32 months; log-rank test, p=0.003). Patients with predominant squamous cell carcinoma component at the leading edge had worse survival than those without it. In conclusion, patients with adenosquamous carcinoma demonstrated worse survival than those with pure adenocarcinoma. S100A2 immunohistochemical staining may be helpful in detecting the squamous component.
Keywords: Adenosquamous carcinoma; S100A2; cholangiocarcinoma; extrahepatic bile duct; prognosis.