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 i n uveal melanoma by determining the relative contribution df all known mech anisms 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 polymer phic microsatellite markers surrounding the p16 locus on chromosom e 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 mela nomas. No evidence of a second region of LOH that did not include the p16 l ocus was found. Four cases had hemizygous losses including markers both dis tal and proximal to p16. Homozygous deletion of the p16 gene was detected i n the 4 remaining cases by microsatellite analysis. Sequence analysis revea led 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 an other without LOH. CONCLUSIONS. p16 inactivation by HD or methylation occurs in 27% of uveal m elanomas, representing the most common molecular genetic alteration identif ied thus far in uveal melanoma.