PROLIFERATING TRICHILEMMAL CYST - REPORT OF 4 CASES, 2 WITH NONDIPLOID DNA CONTENT AND INCREASED PROLIFERATION INDEX

Proliferating trichilemmal cyst (PTC) is an uncommon tumor that usuall y arises on the scalp of elderly women. Its biologic nature is that of a benign lesion with occasional local recurrences. PTC can be confuse d both grossly and microscopically with squamous cell carcinoma and ma lignant PTC. Distinction between these lesions has historically been m ade on a histologic basis. We present four cases of PTC. Histologicall y, the lesions consisted of lobules of basaloid cells admixed with lar ger pale-staining cells with abrupt trichilemmal type of keratinizatio n and peripheral palisading embedded in a fibrous stroma. Flow cytomet ry performed on nuclear extracts of the lesions revealed two of the fo ur lesions to have nondiploid DNA content. Proliferation index, measur ed by immunohistochemical staining with Ki-67 monoclonal antibody alon g with mitotic rate count, was higher in the two nondiploid lesions as compared with their diploid counterparts. The results raise the quest ion of the significance of aneuploidy and increased proliferation indi ces in otherwise benign PTC.