Journal of Clinical Oncology, 2005 ASCO Annual Meeting Proceedings.
Vol 23, No 16S (June 1 Supplement), 2005: 516
© 2005 American Society of Clinical Oncology

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Abstract

Radiation after lumpectomy for DCIS to reduce the risk of invasive breast cancer: A population-based study

Univ of Minnesota, Minneapolis, MN

516

Background: Although randomized trials have demonstrated the efficacy of radiation (RT) in reducing the risk of breast cancer after lumpectomy for Ductal Carcinoma in Situ (DCIS), the use of RT in the population remains relatively low. This study was designed to determine the effectiveness of RT after lumpectomy for DCIS in a population-based fashion using SEER data. Methods: We identified women with DCIS treated with lumpectomy in SEER registry data from 1987 through 1996. We evaluated the effect of RT on development of subsequent invasive breast cancer: the overall rate, the rate of ipsilateral invasive cancer, and the rate of contralateral invasive cancer. Using a proportional hazards model, we evaluated the effect of RT on development of invasive breast cancer over time adjusting for potential confounders. Results: A total of 10,034 women underwent lumpectomy for DCIS in this time period; 5063 underwent lumpectomy only and 4971 underwent RT after lumpectomy. Invasive breast cancer developed in 854 patients; 439 in the ipsilateral breast and 413 in the contralateral breast (laterality unknown in 2 cancers). The actuarial rate of invasive ipsilateral breast cancer at 8 years was 6.2% in the lumpectomy only group and 2.7% in the RT group. The actuarial rate of invasive contralateral breast cancer at 8 years was 4.2% in the lumpectomy only group and 4.0% in the RT group. Lumpectomy only was strongly associated with development of ipsilateral breast cancer over time after adjusting for potential confounders. The adjusted hazards ratio for development of ipsilateral invasive cancer was 0.43 for the RT group, as compared with the lumpectomy only group (95% CI 0.35 to 0.53), indicating that women who did not undergo RT had 2.3 times the risk of developing ipsilateral invasive breast cancer over time. RT after lumpectomy was not associated with development of contralateral invasive cancer. Conclusions: Women with DCIS in the population have a substantial risk of developing invasive breast cancer after lumpectomy. The effectiveness of RT in reducing the risk of ipsilateral cancer in the population is similar to the efficacy of RT found in trials. This supports routine use of RT after lumpectomy for DCIS in the population.

No significant financial relationships to disclose.

Abstract presentation from the 2005 ASCO Annual Meeting