Association of regional intensity of ductal carcinoma in situ treatment with likelihood of breast preservation

IMPORTANCE: Large regional variation exists in the use of radiotherapy after breast-conserving surgery (BCS) for ductal carcinoma in situ (DCIS). Although patients who do not receive initial radiotherapy for DCIS are candidates for subsequent BCS if they experience a second breast event, many undergo mastectomy instead. OBJECTIVE: To examine whether regional practice patterns of radiotherapy for DCIS affect the use of mastectomy in these patients. DESIGN, SETTING, AND PARTICIPANTS: A retrospective analysis of population-based databases (Surveillance, Epidemiology, and End Results [SEER] and SEER-Medicare). Data were obtained for 2679 women in SEER with a diagnosis of DCIS between 1990 and 2011 and for 757 women in SEER-Medicare with a DCIS diagnosis between 1991 and 2009 who had not undergone radiotherapy for DCIS and experienced a subsequent breast cancer or DCIS diagnosis. EXPOSURES: Treatment intensity for primary DCIS (high, medium, low), as defined by separating health service areas (HSAs) into 3 clusters based on radiotherapy use. MAIN OUTCOMES AND MEASURES: Mastectomy vs BCS at a second breast event defined as DCIS recurrence or new invasive cancer. RESULTS: The median (SD) ages of the participants was 64 (13) years for the 2679 SEER population and 79 (6) years for the SEER-Medicare cohort. Residence in an HSA characterized by greater radiotherapy use for DCIS increased the likelihood of receiving mastectomy vs BCS at a subsequent breast event, even among women who had not previously received radiotherapy for DCIS. Adjusted odds ratios for receiving mastectomy were 1.43 (95% CI, 1.10-1.85) and 1.90 (95% CI, 1.27-2.84) in SEER and SEER-Medicare databases, respectively, among women residing in an HSA with the greatest radiotherapy use vs the least, corresponding to an adjusted increase from 40.8% to 49.6%, and from 38.6% to 54.5%. CONCLUSIONS AND RELEVANCE: Areas with more radiotherapy use for DCIS had increased use of mastectomy at the time of a second breast event even among patients eligible for breast conservation. This association suggests that physician-related factors are affecting the likelihood of breast preservation.