Immunohistochemical study of primary and recurrent basal cell and metatypical carcinomas of the skin.

We investigated cell proliferation and expression of cytoskeletal proteins in 32 cases of primary basal cell carcinomas (BCC), 10 cases of recurrent BCC, and 10 cases of metatypical carcinomas (MTC). Paraffin-embedded biopsies were evaluated immunohistochemically with a battery of antibodies. Antibodies to proliferating cell nuclear antigen (PCNA) demonstrated comparatively low numbers of proliferating cells in 25 of 32 cases of primary BCC. In contrast, both recurrent BCC and MTC exhibited three to four times higher levels of proliferating cells than primary BCC. PCNA-positive cells were usually distributed uniformly throughout the lobules; at times, however, they were localized to the outer areas of those neoplasms, with a comparatively low level of proliferation index. Antibodies to keratin 17 strongly stained cells of all BCC cases, and antibodies to keratin 8 reacted with most of them. In contrast, the staining intensity of both types of keratin in MTC was decreased six to eight times as compared with all BCC. In addition, cells of eight BCC and three MTC reacted with antibodies to smooth muscle alpha-actin and myosin, neoplasms that did not differ by the number of PCNA-positive nuclei from carcinomas without contractile proteins. The differences in cell proliferation and keratin expression between BCC and MTC may be useful criteria for further distinguishing these carcinomas. The appearance of contractile proteins in some BCC and MTC may be the result of, or implies, myoepithelial differentiation.