Analysis of p16 (CDKN2/MTS-1/INK4A) alterations in primary sporadic uveal melanoma.

PURPOSE To define more clearly the role of the tumor suppressor gene p16 in uveal melanoma by determining the relative contribution of all known mechanisms of p16 inactivation in this tumor. METHODS A comprehensive genetic analysis of the p16 gene was performed in 33 primary sporadic ciliochoroidal and choroidal melanomas. Fourteen highly polymorphic microsatellite markers surrounding the p16 locus on chromosome 9p21 were used for the microsatellite analysis. Sequence analysis of the p16 gene was performed on those tumors with 9p21 loss of heterozygosity. To investigate methylation as an alternative mechanism of inactivation of p16, methylation-specific polymerase chain reaction was performed on all tumor DNA samples. RESULTS Loss of heterozygosity (LOH) was found in 8 of 33 (24%) uveal melanomas. No evidence of a second region of LOH that did not include the p16 locus was found. Four cases had hemizygous losses including markers both distal and proximal to p16. Homozygous deletion of the p16 gene was detected in the 4 remaining cases by microsatellite analysis. Sequence analysis revealed no p16 mutations in the tumors with hemizygous loss of p16. Methylation of the 5' CpG island of p16 was found in one tumor with 9p21 LOH and in another without LOH. CONCLUSIONS p16 inactivation by HD or methylation occurs in 27% of uveal melanomas, representing the most common molecular genetic alteration identified thus far in uveal melanoma.