To evaluate the preferential histological type of MI-associated mutations in the development of gastric carcinoma, mutations of TGF-beta RII, p53, and p16 were analyzed for the two types of primary gastric carcinomas showing MI.
Transcriptional silencing of the p16 gene in association with methylation of its 5'-CpG island was examined by methylation-specific PCR in 18 pancreatic carcinomas.
Two patients had p16 alterations in PILs matching those of the associated carcinomas. p16 mutations were not found in PILs of pancreata having wild-type p16 in the carcinoma, nor were they found in ducts having normal histology.
Although slightly higher in Japan than in the United States, the frequency of p16 exon deletions in clinical prostatic carcinomas is very low, and probably is not important in the development of this neoplasm.
In contrast, p16 expression was weak in normal endometrium and increased in most cases of hyperplasia, but negative or minimally positive in 74% of the carcinomas and the Hec1B adenocarcinoma cell line, and there was no significant association with Rb immunostaining.
These results suggest that inactivation of p16 is important in the development or progression of at least some salivary duct carcinomas, but we found no evidence that its alteration plays a role in the other subtypes examined.
Changes in DNA methylation may be more important for inactivation of this gene (and perhaps other tumor suppressor genes) in LMP tumors, which lack many of the alternative mechanisms present in carcinomas. p16 expression is primarily related to mucinous differentiation in cystadenomas.
Only 18% of the carcinomas showed a normal level of expression of the four genes tested, and p16 appeared to be the most common target of cell cycle deregulation.
Three of the four antibodies produced nuclear immunoreactivity in 7 to 14 of the 16 carcinomas carrying p16 mutations; G175-405 showed only weak reactivity in one case.
As PCR based approaches analyzing for homozygous deletions could be confounded by unavoidable contributions of normal cells in microdissected tissue, we performed in situ hybridization (ISH) on primary prostate carcinomas to accurately evaluate p16 and p15 copy numbers on a cell-by-cell basis.
DNA isolated from 15 adenomas and 14 carcinomas was examined for methylation of p16 by methylation-specific PCR. p16 methylation was detected in five of 15 adenomas and eight of 14 carcinomas (45% of all tumors).