Surveillance Mammography and Second Primary Breast Cancer Diagnosis Among Older Women With a History of Breast Cancer

Importance Although surveillance mammography is commonly performed among older women, whether this practice improves clinical outcomes in this population is uncertain. Objective To evaluate the association between surveillance mammography and second primary breast cancer stage at diagnosis among older women with a history of breast cancer. Design, Setting, and Participants This retrospective longitudinal cohort study used Surveillance, Epidemiology, and End Results Program–Medicare data. Women with nonmetastatic breast cancer that was diagnosed from 2004 to 2008 at 67 years or older who had a surveillance mammogram at approximately 5 years after diagnosis were included. Analyses used cause-specific hazard models with inverse probability of treatment weighting to estimate the risk of stage-specific second primary breast cancer among women who continued surveillance mammography and those who did not. Analyses were stratified by hormone receptor (HR) status of the initial breast cancer. Follow-up continued until second breast cancer diagnosis, death, or end of the study (December 2021). Analyses were performed between November 2025 and August 2026. Exposure Continued surveillance mammography more than 5 years after initial diagnosis. Main Outcomes and Measures Stage-specific cumulative incidence of a second primary breast cancer, categorized as in situ, localized, or advanced (regional or distant). Results Among 9888 women (mean [SD] age, 81.1 [5.5] years; 387 Hispanic [3.9%], 514 non-Hispanic Black [5.1%], and 8514 White individuals [86.1%]), 8055 (81.4%) had in situ or localized disease and 7621 (76.9%) had HR-positive tumors at initial diagnosis. Overall, 7940 women (80.3%) continued surveillance at cohort entry. Advanced second primary breast cancer was rare, and incidence did not differ among those who continued surveillance and those who did not (cumulative incidence, 1.65% vs 2.15%; hazard ratio, 0.76; 95% CI, 0.46-1.26). Results were similar in subgroups of women with initial HR-positive and HR-negative breast cancer. Conclusions and Relevance The results of this cohort study suggest that among older survivors of breast cancer, continued surveillance mammography was not associated with a reduced risk of advanced second primary breast cancer. The absolute risk of advanced cancer was low, and surveillance decisions should be individualized given the potential burdens of continued surveillance.