Early-age-at-onset colorectal cancer and microsatellite instability as markers of hereditary nonpolyposis colorectal cancer.

PURPOSE: Early-age-at-onset colorectal cancer and microsatellite instability are characteristic features of hereditary nonpolyposis colorectal cancer. Our aim was therefore to investigate whether these features might be useful markers in screening for hereditary nonpolyposis colorectal cancer and mismatch repair gene mutations.

METHODS: From 1,132 consecutive patients who underwent surgery for colorectal cancer at our department between 1980 and 1999, we selected all patients 40 years of age or younger (study group, n = 59) and a subset of patients 40 years of age or older (control group, n = 60) who were matched for gender and pathologic TNM stage. Patients for whom a complete family cancer history or microsatellite status was unavailable were excluded from the study. Family cancer histories, retrieved from archival charts, were reassessed. Microsatellite status was investigated with the five microsatellites from the Bethesda recommended panel (BAT-26, BAT-25, D2S123, D5S346, and D17S250). On the basis of the number of altered microsatellites (> or = 2, 1, or 0), tumors were considered as having high or low instability or microsatellite stability, respectively. Mutation analysis for MLH1 and MSH2 genes was performed only in cases of high instability. DNA was investigated for mutations by single-strand conformational polymorphism and sequencing analysis.

RESULTS: Data from 95 patients (study group: n = 37, 18 males, mean age 35 years; control group: n = 58, 29 males, mean age 62 years) were available for analysis. Four patients (study group, n = 3; control group, n = 1) fulfilled the Amsterdam II criteria for hereditary nonpolyposis colorectal cancer. Of the 37 study group tumors, 12 (32.4 percent) showed high-frequency microsatellite instability, and 25 had microsatellite stability, whereas among the 58 control group tumors, 4 (7 percent) showed high-frequency microsatellite instability, and 54 had microsatellite stability (P < 0.002). Mismatch repair gene mutation analysis was performed in 12 cases (study group, n = 7; control group, n = 5). We found four mutations (MSH2 119delG, MLH1 ex9 684insT, MSH2 Gln239Stop, and MLH1 del0.8 Kb) in the study group patients and none in the control group. Of four hereditary nonpolyposis colorectal cancer patients who underwent mismatch repair gene mutation analysis, one had a mutation.

CONCLUSIONS: Early-age-at-onset colorectal cancer is significantly correlated with high-frequency microsatellite instability tumor status and is a useful criterion to identify hereditary nonpolyposis colorectal cancer patients. Moreover, when used in association with high-frequency microsatellite instability status, it is effective in selecting patients for mismatch repair gene mutation analysis.