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.