Abstract P2-14-04: Genetic testing and bilateral mastectomy for women with breast cancer: Does testing matter more than the test result?
Authors: Verdial FC , Bartek MA , Anderson BO , Javid SH 
Published: May 2019

Abstract
Background: Genetic testing for hereditary breast cancer may allow women with breast cancer to make informed and individualized decisions regarding breast cancer treatment and strategies to reduce the risk of contralateral breast cancer. While rates of bilateral mastectomy (therapeutic mastectomy + contralateral prophylactic mastectomy) among women with unilateral breast cancers are known to be increasing, the factors influencing this decision and the role of genetic testing are poorly understood. We examined bilateral mastectomy rates and factors associated with bilateral mastectomy among women with unilateral breast cancer.
Methods: We identified patients diagnosed with unilateral breast cancer from 2000-2015 from The Health of Women Study, a cohort study led by the Dr. Susan Love Research Foundation. We calculated rates of bilateral mastectomy among women who underwent surgical treatment for breast cancer. We used multivariable logistic regression models to evaluate factors associated with bilateral mastectomy.
Results: Among 2,028 patients who underwent surgery for unilateral breast cancer, 19% underwent bilateral mastectomy. Forty-one percent (n= 84 of 205) of patients who underwent testing and tested positive for a deleterious mutation underwent bilateral mastectomy, compared to 26% (n= 439 of 1,689) of women who tested negative and 12.5% (n= 274 of 2,197) of those not tested. Among those with a negative genetic test, pre-test risk of harboring a genetic mutation (based on family history and age at diagnosis) was not associated with bilateral mastectomy (p=0.250). After adjusting for race, age, level of education, and pre-test mutation risk, the odds of bilateral mastectomy were 69% higher among patients who underwent genetic testing (OR 1.69, 95% CI 1.29–2.22, p&lt;0.001) versus those who did not undergo genetic testing. This finding was consistent regardless of genetic test result.
Multivariable analysis of factors associated with bilateral mastectomy Odds ratio95% Confidence Intervalp valueRisk Category Low riskReference--Moderate risk1.470.96 – 2.420.078High risk1.460.92 – 2.320.111 Genetic testing1.691.29 – 2.22&lt;0.001 Genetic test result Not testedReference--Positive test2.711.66 – 4.46&lt;0.001Negative test1.561.18 – 2.070.002*Adjusted for age, race, and level of education.
Conclusions: Genetic testing among breast cancer patients, regardless of test result or pre-test mutation risk, is significantly associated with bilateral mastectomy. Many women (˜1/4) with a negative genetic test and at low risk of hereditary breast cancer, by family history and age at diagnosis, currently undergo bilateral mastectomy with unclear benefits. Further qualitative research will aim to elucidate reasons driving choice of bilateral mastectomy among women with breast cancer.
Citation Format: Verdial FC, Bartek MA, Anderson BO, Javid SH. Genetic testing and bilateral mastectomy for women with breast cancer: Does testing matter more than the test result? [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-14-04.