Abstract
The first case was an 83-year-old Japanese woman with a tumor on the top of her head, and the second case was a 90-year-old Japanese woman with a tumor on her back. A microscopic examination of the skin lesions revealed multiple lobules consisting of Sudan black stain positive foamy cells and undifferentiated basophilic cells. An electron microscopic examination showed the foamy cells to contain various amounts of lipid droplets, while the undifferentiated cells were rich in cytoplasmic organelles. A diagnosis of extra-ocular sebaceous carcinoma was made. We performed histochemical and immunohistochemical analyses on these 2 cases as well as on 27 basal cell carcinomas, and 16 squamous cell carcinomas for comparative purposes. The tumor cells of sebaceous carcinoma showed a positive reaction for epithelial membrane antigen, human milk fat globules subclass 1 (HMFG 1), and HMFG 2. All the basal cell carcinomas showed a negative reaction for HMFG 1/2. It is often difficult to distinguish sebaceous carcinoma from basal cell carcinoma with sebaceous differentiation, because both tumors have lobules consisting of Sudan black stain positive foamy cells. Our findings indicate that immunohistochemical studies for HMFG 1/2 are very useful for distinguishing these two diseases.
