CDKN2A mutation and deletion status in thin and thick primary melanoma

Human melanoma cell lines and tumor tissue from familial and sporadic melanomas have frequent, nonrandom chromosomal breaks and deletions on chromosome 9p21, a region that includes the tumor suppressor gene CDKN2A/p16INK4A. Germ-line mutations within this gene have been observed in some familial melanoma kindreds, but somatic mutation in sporadic primary melanoma is infrequent. Thirty-nine archival, paraffin-embedded, sporadic, primary cutaneous malignant melanomas (20 >3-mm-thick and 19 <0.75-mm-thick cases) were examined for mutations of the CDKN2A gene using single-strand conformational polymorphism analysis and direct sequencing. No mutations were detected. Loss of heterozygosity for the 9p21 microsatellite marker D9S942 was detected in 6 of 17 informative thick lesions (35%) but 0 of 18 thin lesions (P = 0.006). These results support other studies indicating that intragenic mutation is an infrequent mechanism of CDKN2A inactivation in primary melanoma. The finding of loss of heterozygosity for the 9p21 microsatellite D9S942 in thick but not thin primary melanoma suggests that deletion or inactivation of CDKN2A or other tumor suppressor gene(s) at this locus is involved in the progression rather than initiation of sporadic malignant melanoma.