Double primary malignancy in colorectal cancer patients-MSI is the useful marker for predicting double primary tumors

The incidence of double primary malignancies (DPM) is known to be higher in colorectal cancer patients than the general population. And, the role of microsatellite instability (MSI) in DPM has been previously studied. We evaluated the clinical features and association between MSI and colorectal cancer patients with DPM. From September 1994 to May 2004, we reviewed 2,301 colorectal cancer patients with regard to secondary primary malignancies. A subgroup analysis was performed for MSI after January 2003. One hundred forty-five patients (6.3%) had a DPM identified. In DPM group, 57 patients had a synchronous DPM (39.3%), and 88 patients had a metachronous malignancy (60.7%). Male gender (p < 0.001) and colon cancer (p < 0.001) were the factors related with the development of the DPM. Most of the second malignancies occurred within 3 years after the primary operation. The common second malignancies were stomach (58 patients, 40%) and lung (21 patients, 14.5%). In the subgroup analysis, there was a higher frequency of DPM in the MSI group when compared to the microsatellite stable group (p = 0.021). The careful pre- and postoperative evaluation should be paid for detecting DPM as well as for detecting recurrence in colorectal cancer patients. The results of this study suggest that MSI might be a useful marker for the detection of DPM in colorectal cancer patients.