Beneficial effect of repeated participation in breast cancer screening upon survival.

person Robert A. Smith American Cancer Society, Atlanta, GA info_outline Robert A. Smith, Stephen W Duffy, Amy Ming-Fang Yen, László Tabár, Abbie Ting-Yu Lin, Sam Li-Sheng Chen, Chen-Yang Hsu, Peter Dean, Tony Hsiu-Hsi Chen

Authors person Robert A. Smith American Cancer Society, Atlanta, GA info_outline Robert A. Smith, Stephen W Duffy, Amy Ming-Fang Yen, László Tabár, Abbie Ting-Yu Lin, Sam Li-Sheng Chen, Chen-Yang Hsu, Peter Dean, Tony Hsiu-Hsi Chen Organizations American Cancer Society, Atlanta, GA, Centre for Cancer Prevention, Wolfson Institute of Preventive Medicine, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom, School of Oral Hygiene, College of Oral Medicine, Taipei Medical University, Taipei City, Taiwan, Department of Mammography, Falun Central Hospital,, Falun, Sweden, Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University, Taipei, Taiwan, Master of Public Health Program, College of Public Health, National Taiwan University,, Taipei, Taiwan, University of Turku, Turku, Finland Abstract Disclosures Research Funding Other American Cancer Society Background: The benefit of mammography screening in reducing population mortality from breast cancer is well established. However, the effect of repeated participation at scheduled screens on case survival is less well documented. Methods: In this retrospective analysis of breast cancer survival, we analyzed incidence and survival data on 37,079 women ages 40-69 from nine Swedish counties who had between one and five invitations to mammography screening and were diagnosed with breast cancer between 1992 and 2016. Of these, 4,564 subsequently died of breast cancer. For each breast cancer diagnosed in each county’s period of observation, we obtained data on previous screening history, and subsequent death (or not) from breast cancer. Formal comparisons of survival with respect to numbers of screening exams attended prior to a diagnosis of breast cancer were carried out using Cox proportional hazards regression with time-varying covariates, ie, cumulative numbers of screens, yielding hazard ratios and 95% confidence intervals (CI). We corrected for potential self-selection using the method of Duffy et al, which gives a corrected estimate based on the proportion of participants, the uncorrected estimate, and the relative risk of breast cancer death for non-participants compared to an uninvited population. Results: Depending on number of invitations, 58-73% (average 65%) participated in all scheduled screens, and 73-96% (average 91%) participated in at least one examination. There was successively better survival among women with increasing numbers of screening exams. For a woman with five previous screening invitations who participated in all five screening exams, the hazard ratio was 0.28 (95% CI 0.25-0.33, p<0.0001), a 72% risk of dying from breast cancer, compared to a woman attending none. Following a conservative adjustment for potential self-selection factors, the hazard ratio was 0.34 (95% CI 0.26-0.43, p<0.0001). Conclusions: For those women who develop breast cancer, regular prior participation in mammography screening confers significantly better survival. Most women will not develop breast cancer in their lifetime. These results indicate that for those who do, regular participation in screening considerably improves the probability of surviving it. The distinction between the general, population benefit of mammography screening, and the benefit of regular participation in mammography screening should be clearly articulated in breast cancer screening messaging and decision aids. Hazard ratios by number of screens in which the women participated, unadjusted and adjusted for potential self-selection factors. Number of screens participated in Hazard ratio (95% CI) Unadjusted Adjusted 0 1.00 (-) 1.00 (-) 1 0.71 (0.57-0.89) 0.87 (0.67-1.12) 2 0.50 (0.40-0.63) 0.61 (0.45-0.83) 3 0.37 (0.30-0.46) 0.45 (0.34-0.60) 4 0.37 (0.31-0.43) 0.45 (0.35-0.58) 5 0.28 (0.25-0.33) 0.34 (0.26-0.43)