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Int J Radiat Oncol Biol Phys. 2008 Nov 15;72(4):1021-30. doi: 10.1016/j.ijrobp.2008.02.040. Epub 2008 Jun 14.

Dose to the contralateral breast from radiotherapy and risk of second primary breast cancer in the WECARE study.

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  • 1Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.



To quantify the risk of second primary breast cancer in the contralateral breast (CB) after radiotherapy (RT) for first breast cancer.


The study population included participants in the Women's Environmental, Cancer, and Radiation Epidemiology study: 708 cases (women with asynchronous bilateral breast cancer) and 1399 controls (women with unilateral breast cancer) counter-matched on radiation treatment. Participants were <55 years of age at first breast cancer. Absorbed doses to quadrants of the CB were estimated. Rate ratios (RR) and 95% confidence intervals (CI) were calculated using multivariable-adjusted conditional logistic regression models.


Across all patients, the mean radiation dose to the specific quadrant of the CB tumor was 1.1 Gy. Women <40 years of age who received >1.0 Gy of absorbed dose to the specific quadrant of the CB had a 2.5-fold greater risk for CB cancer than unexposed women (RR = 2.5, 95% CI 1.4-4.5). No excess risk was observed in women >40 years of age. Women <40 years of age with follow-up periods >5 years had a RR of 3.0 (95% CI 1.1-8.1), and the dose response was significant (excess RR per Gy of 1.0, 95% CI 0.1-3.0).


Women <40 years of age who received a radiation dose >1.0 Gy to the CB had an elevated, long-term risk of developing a second primary CB cancer. The risk is inversely related to age at exposure and is dose dependent.

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