Proliferative characterization of basal‐cell carcinoma and trichoepithelioma in small biopsy specimens

We examined the proliferative characteristics of 20 basal-cell carcinomas (BCCs) and 16 trichoepitheliomas (TEps) in an effort to understand and explore possible differences in their tumorigenic cell-cycle properties. These tumors were first compared for their expression of the nuclear proliferative protein Ki-67 and the tumor suppressor protein p53. We also compared the p53 downstream effector, p21(waf-1/cip-1), an inhibitor of cyclin-dependent kinases. The other p53-dependent, cyclin-dependent kinase inhibitor, p27(kip-1), has shown to be increased in TEps, which is consistent with this benign neoplasm's better-differentiated state. In our findings, we confirmed through immunohistochemical staining for Ki-67 that BCCs qualitatively showed a greater proliferative fraction compared to TEps (50.0 vs. 13.0%, p < 0.00001) as well as over-expression of p53 (2+ vs. 1+, p < 0.0008). BCCs marked by p21 demonstrated scattered nuclear positivity compared to the virtual absence of staining in the TEps (p < 0.019). In studying their cell-cycle properties, our findings suggest that abnormalities in the p53 pathway allow BCCs to obtain a growth advantage. We show that Ki-67 and p53 staining both appear useful in resolving challenging differential diagnoses and thereby help in directing appropriate treatment strategies.