Epidemiology of familial adenomatous polyposis in Sweden: Changes over time and differences in phenotype between males and females

Background: The: Swedish Polyposis Registry was set up in Sweden in the lat e 1950s to promote screening of familial adenomatous polyposis (FAP). The a im of this study was to examine the epidemiology of FAP in Sweden, includin g the influence of screening on morbidity and mortality in colorectal cance r (CRC). Methods: Four hundred and thirty-one patients (213 males and 218 f emales) with FAP from 145 families recorded by the Swedish Polyposis Regist ry were investigated. The effect of screening on morbidity and mortality in CRC was evaluated by comparing the 216 probands with the 215 call-up patie nts. Three different periods were studied: the pre-screening period (1912-1 956), the first screening period (1957-1976), and the second screening peri od (1977-1996). Results: The mean annual incidence rates during the three p eriods were 0.2, 1.38, and 0.86 per million, respectively. The birth freque ncy was calculated to be I in 18,000 between 1947 and 1966, and the prevale nce was 32 per million at the end of 1996. The proportion of new mutants am ong the FAP patients born between 1927 and 1966 was estimated to be 11%. Th e median age at diagnosis of probands was 39 (range, 11-71) years and did n ot change over time, although an increase was seen in the subgroup with CRC at diagnosis (P = 0.02). In the call-up group the median age at diagnosis was 22 (range, 3-65) years. Sixty-seven per cent of the probands and 3.3% o f the call-up patients had CRC at diagnosis, and the corresponding mortalit y figures were 44% and 1.9%. The risk among probands of having CRC at diagn osis decreased from 81% to 49% (P = 0.0006). Female probands were diagnosed with symptoms (P = 0.03) and CRC (P = 0.04) earlier than male probands. Co nclusions: A nationwide screening program facilitates detection and early d iagnosis of FAP. A decrease in CRC morbidity among probands contributed to the improved prognosis. An earlier onset of symptoms and CRC in females ind icate that the course of FAP is influenced by sex.