Characterization of mutator phenotype in familial colorectal cancer patients not fulfilling amsterdam criteria.

PURPOSE

Although the mutator phenotype, including genetic and epigenetic alterations of the mismatch repair (MMR) system, seems to be pronounced in familial colorectal cancer, there have been few integrative studies comprising the entire mutator pathway. This study was done to identify the entire mutator pathway determining risk factors in patients with familial colorectal cancer not fulfilling the Amsterdam criteria.

EXPERIMENTAL DESIGN

We consecutively recruited 134 colorectal cancer patients with a family history of accompanying cancers. Patients with hereditary nonpolyposis colorectal cancer meeting the Amsterdam criteria, familial adenomatous polyposis, or those receiving preoperative radiotherapy were excluded. Mutator phenotype was assessed by assaying microsatellite instability (MSI) at 24 markers, hMLH1-promoter methylation, mutations at MMR genes (hMLH1, hMSH2, hMSH6, and hPMS2), and immune staining of MMR proteins (hMLH1, hMSH2, hMSH6, hPMS1, and hPMS2).

RESULTS

Of the 208 cancers in first-degree and/or second-degree relatives of patients, colorectal and gastric cancers (81%) were most common. Of the 134 proband colorectal cancers, 23 (17%) were MSI in high level, and 32 (24%) were MSI in low level. MMR alterations, including known polymorphism and splicing substitution, were identified in eight patients (6%). Twenty-eight tumors with mutator phenotype were further identified by hMLH1-promoter methylation and/or loss of MMR protein expression. In 51 tumors (38%), mutator phenotype was associated with right-sided colon cancer (P < 0.001) and younger age at onset (P=0.032), but the number of patients with a mutator phenotype did not differ with respect to inheritance patterns of accompanying cancers, either successive or horizontal transmission (P=0.815). Familial impact value, which differentially associated the degree of relatives with all accompanying cancers, effectively discriminated MSI in high level from microsatellite stable/MSI in low level tumors.

CONCLUSION

Familial colorectal cancer may be associated with multiple occurrences of colorectal or accompanying cancers inherited by dominant or recessive transmission. MMR gene mutations, however, are less associated with mutator phenotype in familial colorectal cancer.