Five-year annual incidence and clinico-molecular features of breast cancer after the last negative screening mammography at age 68-69

Abstract

Objective: The European Commission Initiative on Breast Cancer recommendation for triennial screening of women aged 70-74 is based on very weak evidence. A cohort of Italian women who had their last biennial screening mammography at age 68-69 was followed up for 5 years, assumed to represent the interval to another hypothetical screening mammography, in order to determine the annual proportional incidence of interval breast cancer.

Methods: The cohort included 118,370 women. They had their last mammography between 1997 and 2008. Incident breast cancers were identified by record-linking the cohort with the regional breast cancer registry. The expected incidence in the age range 65-74 was estimated with an age-period-cohort model. The number of interval cancers was divided by the expected number to obtain their proportional incidence.

Results: Overall, there were 298,658 woman-years at risk with 371 interval cancers versus 988.8 expected. In the first, second, third, fourth, and fifth interval year, the proportional incidence was 0.09 (95% confidence interval, 0.06-0.13), 0.32 (0.25-0.39), 0.60 (0.49-0.73), 0.75 (0.60-0.92), and 0.81 (0.60-1.07), respectively. Between the second and the fifth year, tumour stage and molecular subtype did not change significantly.

Conclusion: Though not supported by these findings, the proposal of triennial screening for women aged 70-74 merits further research, because the 95% confidence interval of the third-year proportional incidence of interval cancer included 0.50-the maximum limit considered acceptable for women aged 50-69.

Key points: • The third-year incidence of breast cancer relative to the expected one was 0.60 (95% confidence interval, 0.49-0.73). • Between the second and the fifth year, tumour stage and molecular subtype did not change significantly (p >0.10). • The proposal of a 3-year screening interval at age 70-74 merits further evaluation.

Keywords: Breast neoplasms; Interval cancer; Mammography; Mass screening; Proportional incidence.