The frequency of synchronous or metachronous multiple primary carcinomas in patients with gastrointestinal carcinoma or colorectal carcinoma (CRC) has been reported to be ≈10%. We determined the role of hMSH2 and hMLH1 in double carcinomas with both GC and CRC. Fifty-six patients with synchronous or metachronous colorectal carcinoma with gastric carcinoma (CRC with GC), and 69 patients with CRC alone was included in our study. We investigated their clinicopathological characteristics, family history and immunohistochemical stains of hMSH2 and hMLH1 were compared between the patients with CRC alone and those with both CRC with GC. The defective protein expression of hMSH1 and/or hMLH1 in colorectal carcinomas was significantly higher in patients with both CRC with GC than in those with CRC alone (p<0.0001). The survival rate in patients with both CRC with GC was significantly lower than that in those with CRC alone (p<0.01), in addition, the survival rate in patients with defective protein expression of hMSH2 and/or hMLH1 was higher than in those with a positive protein expression of hMSH2 and/or hMLH1 in CRC with GC (p<0.05). The incidence of defective protein expression of hMSH2 and/or hMLH1 in CRC with GC patients suggests that abnormalities in the function of hMSH2 and hMLH1 may play an important role in carcinogenesis. Our findings indicate that the CRC patients who demonstrate a defective protein expression of hMSH2 and/or hMLH1 have a higher risk of developing secondary carcinoma in the gastrointestinal tract.

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