An alpha-fetoprotein-producing carcinoma of the rectum.

A rare alpha-fetoprotein (AFP)-producing carcinoma that originated in the rectum of a 54-year-old man is reported. High levels of AFP are found in the serum (5,126 ng/ml) and homogenate of the tumor tissue (2,600 ng/g). Two morphologic patterns were noted in the tumor. One was that of well differentiated tubular adenocarcinoma and the other was more polymorphous, in which the tumor cells grow in a solid-sheet with occasional glandular and papillary structures. Hyaline bodies and Schiller-Duval body-like structures were also found in the polymorphous area. There was a gradual transition between the well differentiated and the polymorphous area. AFP was positive in the polymorphous area and negative in the well differentiated area on immunohistochemical examination. These morphologic and immunohistochemical characteristics may suggest a differentiation toward embryonal carcinoma of the polymorphous component. Moreover, the polymorphous component showed marked vascular invasion and metastasis of liver as well as regional lymph nodes. AFP-producing carcinoma cells may be more aggressive than ordinary adenocarcinoma.