Immunohistochemical study of mixed tumor of the skin with marked ossification.

We observed an unusual case of mixed tumor of the skin associated with marked ossification on the upper lip of a 68-year-old Japanese woman. The tumor was a well-circumscribed mass that measured 3 x 3 x 2 cm and contained exuberant bone formation with a marrow-like structure. Histological examination of the tumor showed that the bones occupied a quarter of the specimen. Except for the large bone formation, the tumor showed typical features of a tubulocystic type of mixed tumor. The bone was formed without intervening cartilage, suggesting the possibility of the direct deposition of osteoid by metaplastic cells. To our knowledge, no similar case of mixed tumor of the skin associated with marked bone formation has been reported.