The frequency of ipsilateral second tumors after breast-conserving surgery for DCIS: a population based analysis.

BACKGROUND The diagnosis of ductal carcinoma in situ (DCIS) is increasing, although to the authors' knowledge there is no consensus regarding optimal treatment. This analysis of women treated with breast-conserving surgery (BCS) evaluated the impact of radiation therapy (RT) in patient outcomes. METHODS The current study included a population-based sample of 1103 women residing in selected Surveillance, Epidemiology, and End Results (SEER) registries who were diagnosed with DCIS between 1991–1992. Data were obtained from the registry, physician follow-up, and pathology reports. Physicians were contacted in 1999 to determine whether the patient had developed a second event in the ipsilateral breast. For second events, pathology reports were reviewed to determine the presence of in situ or invasive disease. Registry data through 2001 were used to assess death rates and cause of death. Cox proportional hazards and logistic regression models were used to evaluate the rates of second events and breast carcinoma deaths between women treated with and without RT. RESULTS Over an average of 91 months, 13.2% of women developed a second event. Rates of second events were 11% for women treated with BCS and RT compared with 15% for women treated with BCS only (adjusted hazards ratio, 0.64; 95% confidence interval, 0.44–0.92). Women receiving RT were significantly less likely to develop invasive breast carcinoma in the ipsilateral breast (adjusted odds ratio, 0.40). By 2001, the rate of death from breast carcinoma was 2.7%; in the group of women treated with BCS only compared with 0.8% in the group of women treated with BCS with RT. CONCLUSIONS Among a population-based cohort, RT was found to significantly reduce the risk of second events in the ipsilateral breast, particularly invasive tumors, although not to the extent reported in clinical trials. Cancer 2005. © 2005 American Cancer Society.