Epidemiology of familial adenomatous polyposis in Finland: impact of family screening on the colorectal cancer rate and survival.

The incidence and prevalence rates of familial adenomatous polyposis (FAP) in Finland between 1961 and 1990 were estimated from Finnish polyposis registry data comprising 81 FAP families, including 251 affected patients. In addition, the effect of family screening on the occurrence of colorectal carcinoma was evaluated by comparing the call up and proband groups and calculating the proportion of FAP among all patients with colorectal carcinoma. The incidence of FAP was 0.62 to 2.38 per million and the prevalence increased steadily from 0.88 to 26.3 million during the study period suggesting improving prognosis. Altogether 76 of 116 probands (65.5%) had colorectal carcinoma compared with only five of 76 call up patients (6.6%). Consequently, the life expectancy of the call up patients was significantly better than that of the probands from the age of 31 years and above. However, at most, 0.53% of all colorectal carcinomas were associated with FAP in 1966-70, and the diminishing frequency of this proportion was more a result of an increase in sporadic colorectal carcinomas in Finland than of family screening for FAP. Family screening is very effective in FAP and must always be undertaken when a new proband is diagnosed.