Allelic imbalance studies of chromosome 9 suggest major differences in chromosomal instability among nonmelanoma skin carcinomas.

CONTEXT Loss of heterozygosity in the 9p21-p22 region, has been frequently described in a wide range of human malignancies, including familial melanomas. Also, losses and gains in other regions of chromosome 9 have frequently been observed and may indicate additional mechanisms for basal cell tumorigenesis. OBJECTIVE To investigate allelic imbalance in the 9p21-p22 region, among basal cell carcinomas. TYPE OF STUDY Microsatellite analysis. SETTING Two dermatology services of public universities in São Paulo and the Laboratory of Cancer Molecular Genetics of Universidade Estadual de Campinas (Unicamp). PARTICIPANTS 13 patients with benign skin lesions consecutively referred to the outpatient dermatology clinics of Unicamp and Universidade Estadual de São Paulo (Unesp) and 58 with malignant skin tumours. MEAN MEASUREMENTS: We examined 13 benign cases including four of solar keratosis, three keratoachanthomas, three melanocytic nevi, two of Bowen's disease and one of neurofibroma, and 58 malignant skin tumors: 14 of squamous cell, 40 basal cell carcinomas and four melanomas. Participating patients had the main tumor and a normal portion of non-adjacent skin surgically removed. DNA was extracted from the tumor and matching normal tissue. We used four sets of primers to amplify polymorphic microsatellite repeats on chromosome 9, two of them targeting the 9p21-p22 region. RESULTS We identified eight cases (20%) of allelic imbalance among basal cell carcinomas, two cases of loss of heterozygosity and six cases of microsatellite instability in the 9p21-p22 region. Additional markers were also involved in three of these tumors. No events were detected among the benign or the other malignant cases. CONCLUSION This phenotype dependency suggests that there is a major distinction between the two most important forms of nonmelanoma skin cancers in their tendency to present microsatellite instability in chromosome 9. Since the CDKN2a/p16INK4a, p19ARF and p15INK4b tumor suppressor genes do not appear to be responsible for the observed abnormalities, other genes at 9p21-p22 may be involved in the pathogenesis and progression pathway of basal cell carcinomas.