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.