Colon cancer tissue was assayed using immunohistochemistry for expression of hMLH1 and hMSH2, and a panel of five pairs of microsatellite primers (NR21, NR22, NR24, BAT25, and BAT26) for MSI-H analysis and additional dinucleotide markers (D17S250, D5S346, and D2S123) used for MSI-L.
A family history of breast/ovarian, HNPCC or colon cancer in a first degree relative was found in 40% of fallopian, 20% of biliary, 35% of pancreatic, 27% of urothelial and 20% of small bowel cancer patients.
A smaller 7-gene panel showed high sensitivity and specificity in identifying BRAF-mutant, CpG island methylator phenotype high, and MLH1-silenced colon cancers.
A subset of sporadic colon cancers has been shown to have microsatellite instability caused by an epigenetic inactivation of the MLH1 gene by hypermethylation of the the CpG island in its promoter region.
A total of 864 tumors from individuals with colon cancer from Utah and Northern California were evaluated by methylation-specific polymerase chain reaction of CpG islands in hMLH1, methylated in tumors (MINT) 1, MINT 2, MINT 31, and CDKN2A (p16).
Aberrant methylation of the promoter CpG island of hMLH1 is associated with gene silencing in colon cancer and gastric cancer with microsatellite instabilities (MSI).
Among all the 32 families with mutations, families with hMSH2 mutation had a higher ratio of synchronous and metachronous colon cancers than families with hMLH1 mutation (33 vs. 6%, P=0.04).
Among the original 519 patients, nine (all with colon cancer in the family) were diagnosed with HNPCC at the outset-six with MLH1 and three with MSH2 mutations.
Amongst the important known susceptibility genes are those dominant genes conferring a high risk of breast and ovarian cancer (BRCA1), colon cancer (hMSH2 and hMLH1), and melanoma (MLM).
Approximately one quarter of colon cancers with deficient MMR (dMMR) develop as a result of an inherited predisposition syndrome, Lynch syndrome (formerly known as HNPCC).
Defects in MMR genes are known to be crucial for familial form of colorectal cancer but our findings suggest that specific genetic variations in MLH1 are important also in the individual predisposition to sporadic colon cancer.