The histopathology of the skin basal cell carcinoma with areas of intermediate differentiation. A metatypical carcinoma?
The histopathology of the skin basal cell carcinomas (BCCs) with areas of intermediate differentiation (ID) has been investigated. In a series of 127 BCCs, areas of ID were found in 28 tumors (22%), and also in an additional 10 cases of other series. These areas consisted of compact masses of cells without peripheral palisading, and with intermediate differentiation between basal and squamous cells. In comparison with the common undifferentiated BCCs, the BCCs with the ID areas may behave in a more aggressive fashion, since they displayed more precocious ulceration in small tumors (p less than 0.001), greater infiltrative features (p less than 0.001), more atypical cells (p less than 0.001) with increased nuclear-cytoplasmic ratio and more mitoses (p less than 0.001). The relation of such basal cell carcinomas to the metatypical carcinoma of the skin was discussed. Metatypical carcinoma, however, has been poorly defined and thus has no general acceptance in the literature. The new definition of the basosquamous cell carcinoma and the presence of intermediate areas of differentiation in this tumor were emphasized, and it was suggested that metastatic basal cell carcinoma and metatypical carcinoma may be the same tumor.