Familial aggregation of tumors and detection of hereditary non-polyposis colorectal cancer in 3-year experience of 2 population-based colorectal-cancer registries.

The clinical data of 2 population-based registries, located in areas with different incidence rates of colorectal cancer, were used in order to assess the role of familial factors in the pathogenesis of these tumors. The occurrence of tumors in family members was investigated in 389 subjects with colorectal cancer registered in Modena (Northern Italy, an area characterized by a high incidence of colorectal malignancies) between 1984 and 1986; similar information was obtained in 213 patients with tumors of the large bowel registered in Ragusa (Sicily, Southern Italy, an area of similar magnitude and with low incidence rates for these tumors) in the 3-year period 1988 to 1990. In both series, colorectal cancer occurred significantly more often among relatives of patients. Controls were patients of the same sex and age (+/- 5 years) hospitalized during the study periods, but not for gastrointestinal or neoplastic diseases. There were 89 cancer cases (3.1%) among 2,851 relatives of patients in Modena, vs. 17 cases among 1,744 relatives (1.0%) in Ragusa (p < 0.01). Apart from colorectal cancer, there was no excess of other types of tumors in patients' families (in both series). During the 3 years of registration, 17 cases of hereditary non-polyposis colorectal cancer (HNPCC, or Lynch syndrome) were diagnosed in Modena; in contrast, this syndrome was more rare in Ragusa (one case only during 3 years of observation). Similarly, many more families with clinical suspicion of HNPCC were recorded in Northern regions (44 vs. 10). Although incidence rates of colorectal cancer are appreciably higher in Northern than in Southern Italian regions, the excess of this cancer type among close relatives is similar. However, full-blown HNPCC or suspected Lynch syndrome were significantly more frequent in Northern Italy.