VALIDITY OF BREAST-CANCER REGISTRATION FROM ONE HOSPITAL INTO THE SWEDISH NATIONAL CANCER REGISTRY 1971-1991

To validate the Swedish Cancer Registry concerning breast tumours in f emale residents of Malmo 1971-1991, registry-entries were compared wit h clinical records, Correctness and completeness of entries was determ ined for invasive breast cancer (BC) and cancer in situ of the breast (CIS). As BC were registered 3 646 tumours. Of these 3 403 (93.3%) wer e confirmed as BC. Completeness was good with 1.1% of diagnosed tumour s missing. Correctness of registered cases of CIS was 93.3%, but compl eteness only 63.3%, Most missing cases were registered as BC. In bilat eral cancer correctness was 78.0% and completeness 77.2%, All aspects of registration improved during the period. Most differences between d iagnosed and registered cases were due to coding CIS of intraductal ty pe as BC, This practice changed in 1980 resulting in improved precisio n. Using registry data for epidemiological research the question of th eir validity must be addressed. Special consideration should be paid t o coding practice at the registry.