Dose to the contralateral breast from radiotherapy and risk of second primary breast cancer in the WECARE study.
OBJECTIVE
To quantify the risk of second primary breast cancer in the contralateral breast (CB) after radiotherapy (RT) for first breast cancer.


METHODS
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.


RESULTS
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).


CONCLUSIONS
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.
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Marilyn
M
Stovall
Susan A
SA
Smith
Bryan M
BM
Langholz
John D
JD
Boice
Roy E
RE
Shore
Michael
M
Andersson
Thomas A
TA
Buchholz
Marinela
M
Capanu
Leslie
L
Bernstein
Charles F
CF
Lynch
Kathleen E
KE
Malone
Hoda
H
Anton-Culver
Robert W
RW
Haile
Barry S
BS
Rosenstein
Anne S
AS
Reiner
Duncan C
DC
Thomas
Jonine L
JL
Bernstein
D000328:Adult; D001822:Body Burden; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000532:radiotherapy*; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D016609:Neoplasms, Second Primary / Q000453:epidemiology*; D011878:Radiotherapy / Q000706:statistics & numerical data*; D011879:Radiotherapy Dosage; D012062:Relative Biological Effectiveness; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D016896:Treatment Outcome; D014481:United States / Q000453:epidemiology; D016387:Women's Health