This study was performed to evaluate the status of p16 tumor suppressor gene in 25 endometrial carcinomas (ECs) and to correlate the loss of heterozygosity (LOH) at p16 locus, the presence of inactivating mutations, the methylation status of the promotor, and the expression of p16 protein with clinicopathological parameters.

Methylation-specific PCR (MSP) distinguishes unmethylated from methylated alleles in a given gene on sequence changes produced after bisulfite treatment of DNA. Allelic losses were determined at two polymorphic dinucleotide repeat microsatellite markers of the p16 gene on chromosome 9p21 that included D9S974 and D9S1748 at CDKN2A. Mutations were analyzed by exons 1 and 2 of p16 PCR-SSCP. Immunohistochemical staining for p16 protein was performed. The associations between genetic alterations of the p16 and the clinicopathological parameters of ECs were evaluated by chi-squared or Fisher's extraction tests.

The median age of the 25 cases was 52 years, ranging from 32 to 72. The median tumor size was 3.6 cm, ranging from 0.8 to 9.5 cm. Histologically, the ECs were 21 endometrioid, 2 adenosquamous, 1 secretory and 1 papillary serous types. Nine cases of p16 protein staining were negative or minimal positive in 25 ECs (36%). Allelic losses were found in 6 loci (66.7%) of 5 ECs without p16 protein expression (Fisher's extraction test, p=0.0029), In this study, only 2 of 25 ECs (8%) disclosed mutations. Non-endometrioid (secretory and adenosquamous) carcinomas showed more frequent mutation and methylation than endometrioid carcinomas (p=0.043) and high grades (G3, p=0.018) showed more frequent mutation and methylation than low grade ECs.

This study suggests that methylation of p16 promoter region seems not to be common (only 9.5% in our present series) and not to be associated with loss of nuclear p16 protein expression. Loss of p16 protein indicates a higher frequency of LOH, which contributes to the development of high grade or aggressive ECs. The mechanism of p16 inactivation is not clear, so other genetic or nongenetic mechanisms for inactivation should be further studied.