Objective To estimate the proportional incidence (PI) of first- and second-year interval breast cancer among women aged 45–49. Methods In the Emilia-Romagna Region (northern Italy), women aged 45–49 are invited to mammography screening annually, and women aged 50–74 biennially. For younger ones, the proportional incidence of interval cancer in the first and unique interval year was calculated using standard methods. For the second, hypothetical year, it was estimated using two different estimates of the ratio between the second- and the first-year proportional incidence observed among women aged 50–54. Overall, 567,151 negative mammography records were used. Results In the first interval year, the observed proportional incidence of interval cancer among women aged 45–49 was 0.27 (95% confidence interval (CI), 0.22–0.33), within the European limit considered desirable for women aged 50–69 (<0.30). In the second, hypothetical interval year, the estimated proportional incidence ranged from 0.61 (95% CI, 0.43–0.86) to 0.48 (95% CI, 0.31–0.76) depending on whether the estimate was based on data from the pre-digital or digital era, respectively. Conclusion The more up-to-date estimate of 0.48, slightly below the maximum limit considered acceptable for women aged 50–69 (<0.50), suggests that a screening interval of two years may also be an acceptable option for women aged 45–49.
Quality of mammography screening in the Milan programme: Evidence of improved sensitivity based on interval cancer proportional incidence and radiological review