SELF-SELECTION FOR MAMMOGRAPHY AND BREAST-CANCER INCIDENCE BY STAGE

Aims and Background: In the field of breast cancer control, obtaining population-based data on spontaneous mammography (MG) screening should be a priority. This study focuses on the breast cancer incidence and stage distribution in relation to MG use in Ravenna (Italy), 1987-88. Methods: We estimated the MG rates, expected (E) incidence based on mo rtality data, observed (O) incidence, predicted excess incidence based on MG rates, observed excess incidence, and stage distribution accord ing to the MG history. Results: The highest MG rate (37%) was found am ong residents aged 40-44 but none of these had a T1(a-b)NO breast canc er diagnosed nor was the predicted excess incidence demonstrated. Betw een 45 and 64 years, 80% of self-selected screenees had repeat (''inci dence'') MG and the O:E incidence ratio was 1.32 (95% CI 1.09-1.58). T he observed excess incidence was 3.8-fold (95% CI 2.56-5.16) greater t han that predicted. Advanced (T2+ and/or N1+) cases accounted for 42% of patients diagnosed within 3 years of their last MG, for 55% of thos e diagnosed more than 3 years after their last MG, and for 70% of thos e with no previous MG. Above age 70, a significant worsening of stage at diagnosis was associated with a clearcut drop in the proportion of breast cancer patients with previous self-referral for MG. Conclusions : The results indicate that self-selection and its implications are ma jor features of spontaneous screening practice.