Synchronous colorectal cancer: clinical, pathological and molecular implications.

Synchronous colorectal carcinoma refers to more than one primary colorectal carcinoma detected in a single patient at initial presentation. A literature review has shown that the prevalence of the disease is approximately 3.5% of all colorectal carcinomas. This disease has a male to female ratio of 1.8:1. The mean age at presentation of patients with synchronous colorectal cancer is in the early half of the seventh decade. Patients with inflammatory bowel diseases (ulcerative colitis and Crohn's disease), hereditary non-polyposis colorectal cancer, familial adenomatous polyposis and serrated polyps/hyperplastic polyposis are known to have a higher risk of synchronous colorectal carcinoma. These predisposing factors account for slightly more than 10% of synchronous colorectal carcinomas. Synchronous colorectal carcinoma is more common in the right colon when compared to solitary colorectal cancer. On pathological examination, some synchronous colorectal carcinomas are mucinous adenocarcinomas. They are usually associated with adenomas and metachronous colorectal carcinomas. Most of the patients with synchronous colorectal cancer have two carcinomas but up to six have been reported in one patient. Patients with synchronous colorectal carcinoma have a higher proportion of microsatellite instability cancer than patients with a solitary colorectal carcinoma. Also, limited data have revealed that in many synchronous colorectal carcinomas, carcinomas in the same patient have different patterns of microsatellite instability status, p53 mutation and K-ras mutation. Overall, the prognosis of patients with synchronous colorectal carcinoma is not significantly different from that in patients with solitary colorectal carcinoma, although a marginally better prognosis has been reported in patients with synchronous colorectal carcinoma in some series. A different management approach and long-term clinical follow-up are recommended for some patients with synchronous colorectal cancer.