Immunohistochemical analysis of human milk fat globulin 1 and cytokeratin expression in median raphe cyst of the penis.

Because median raphe cyst of the penis shares histological findings with apocrine cystadenoma, some cases were thought to be erroneously reported as apocrine cystadenoma of the penis. Further, there is some controversy as to whether the entity, apocrine cystadenoma of the penis, exists or not. Nine cases of median raphe cyst which were clinically unequivocal from their location on the ventral aspects of the penis, were analysed immunohistochemically by using an antibody against human milk fat globulin 1 (HMFG) and a panel of monoclonal anti-cytokeratin antibodies. HMFG expression was not observed in eight out of nine cases of median raphe cyst of the penis, and the remaining case showed a faint expression of HMFG focally in its luminal surface, while conventional apocrine cystadenoma in extra-genital area expressed HMFG definitively in our previous study. Our results suggest a possibility that apocrine cystadenoma of the penis is very rare or not present. Therefore, we thought that HMFG expression should be examined in the cases in which apocrine cystadenoma on the penis is reported.