PROGRESSION OF BASAL-CELL CARCINOMA THROUGH LOSS OF CHROMOSOME-9Q ANDINACTIVATION OF A SINGLE P53 ALLELE

Basal cell carcinoma (BCC) of the skin represents a unique group of tu mors strongly associated with exposure to UV light. Unlike squamous ca rcinoma of the skin, BCC is generally indolent, noninvasive, and rarel y metastatic. To study the involvement of tumor suppressor genes in th ese neoplasms, we analyzed 36 BCCs for p53 mutations and a subset of t hese tumors for loss of chromosomes 17p and 9q. Sixty-nine % of sporad ic BCCs had lost a 9q allele, with the common area of loss surrounding the putative gene for nevoid BCC or Gorlin's syndrome. Forty-four % ( 16 of 36) of BCCs had a mutated p53 allele, usually opposite pyrimidin e tracts, which is consistent with UV-induced mutations. Surprisingly, only one tumor had lost a 17p allele, and in all BCCs only one p53 al lele was inactivated. This is in direct contrast to other epithelial t umors, which usually progress by the inactivation of both p53 alleles.