The role of hMLH1 methylation in the development of synchronous sporadic colorectal carcinomas.
OBJECTIVE
AB. B. subset of sporadic colorectal carcinomas show microsatellite instability, usually as a result of biallelic hMLH1 gene promoter methylation. Synchronous tumors occur in up to 5 percent of patients with colorectal cancer, but their cause is poorly understood. We hypothesized that in the setting of sporadic microsatellite instability cancers, synchronicity may reflect a global predisposition of colorectal epithelium toward tumor development because of gene hypermethylation.


METHODS
We identified 14 individuals with 33 synchronous cancers from a series of 362 patients with 381 sporadic colorectal cancers. We then analyzed the synchronous lesions for microsatellite status, hMLH1 protein expression, and hMLH1 promoter methylation.


RESULTS
Seven of 33 synchronous tumors (21 percent) showed microsatellite instability, compared with 36 of 348 solitary tumors (10.3 percent, P = 0.06). The 14 patients with synchronous tumors were significantly older than those with solitary tumors (mean age 79.4 vs. 68.2 years, P = 0.01), and 5 of these patients had at least one microsatellite instability tumor. However, only one patient harbored synchronous tumors that were all of the microsatellite instability type. Methylation of the hMLH1 promoter was seen in 9 synchronous cancers from 27 assessable lesions in 7 patients and was associated with microsatellite instability (P = 0.01), right-sidedness (P = 0.01), and loss of expression of hMLH1 (P = 0.03). Only one case showed methylation in all synchronous tumors, whereas in five cases synchronous tumors showed different methylation status within the one individual.


CONCLUSIONS
Our data suggest that synchronous tumors arise as independent events and that the slightly greater frequency of synchronous tumors in individuals with microsatellite instability cancers is likely to be a chance event reflecting the older age of these individuals rather than arising from a predisposition toward cancer as a result of global hypermethylation of colorectal epithelium.
Norrie
Mark W A
MW
Department of Medical Oncology, St. Vincent's Hospital, Darlinghurst, Australia.
Hawkins
Nicholas J
NJ
Todd
Alison V
AV
Meagher
Alan P
AP
O'Connor
Terence W
TW
Ward
Robyn L
RL
D048868:Adaptor Proteins, Signal Transducing; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D020137:Base Pair Mismatch; D002352:Carrier Proteins; D016009:Chi-Square Distribution; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D004260:DNA Repair; D004273:DNA, Neoplasm / Q000235:genetics; D005260:Female; D006801:Humans; D008297:Male; D018895:Microsatellite Repeats / Q000235:genetics*; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics*; D009367:Neoplasm Staging; D009378:Neoplasms, Multiple Primary / Q000235:genetics* / Q000473:pathology; D009687:Nuclear Proteins; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D011446:Prospective Studies
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004273:DNA, Neoplasm; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1