Many women who have experienced a diagnosis of primary breast cancer, including those with ductal carcinoma in situ (DCIS), opt for bilateral mastectomy as their initial treatment. The rationale for choosing bilateral mastectomy is their worry of a potential contralateral breast cancer. Another driver in their decision are the misconceptions among the medical community regarding the risks and benefits of contralateral mastectomy. This worry is accentuated among young patients and those with early-stage disease despite consensus guidelines discouraging the procedure in women of average risk.
It is established that removal of the unaffected breast reduces the incidence of second primary cancers, but studies to date have not shown a decline in breast cancer mortality. Decision-making must be based on the best available risk prediction, including genetic testing (BRAC 1/2) in case of familial predisposition. Personalized knowledge of the risk of contralateral cancer and the benefit of bilateral mastectomy may facilitate counseling for women who are considering a bilateral mastectomy for the treatment of unilateral breast cancer.
A study by Giannakeas, V. et al from the Women’s College Hospital and University of Toronto, Ontario, Canada was conducted to determine whether bilateral mastectomy for treatment of unilateral breast cancer reduces the 20-year risk of breast cancer mortality. The study sample included 661 270 women with unilateral breast cancer (stage 0 to stage III) (invasive and ductal carcinoma in situ) who were diagnosed from 2000 to 2019. Three closely matched cohorts of equal size (36,028) were generated according to surgical approach (lumpectomy vs unilateral mastectomy vs bilateral mastectomy). The cohorts were followed up for 20 years for contralateral breast cancer and the 20-year cumulative risk of breast cancer mortality for each group.
During the 20-year follow-up, there were 766 contralateral breast cancers observed in the lumpectomy group, 728 contralateral breast cancers in the unilateral mastectomy group, and 97 contralateral cancers in the bilateral mastectomy group. The cumulative breast cancer mortality was 32.1% at 15 years after developing a contralateral cancer and was 14.5% for those who did not develop a contralateral cancer. Deaths from breast cancer totaled 3077 women (8.54%) in the lumpectomy group, 3269 women (9.07%) in the unilateral mastectomy group, and 3062 women (8.50%) in the bilateral mastectomy group.
Their major findings were (1) contralateral breast cancer was equally frequent in the lumpectomy and unilateral mastectomy groups, with approximately 7% cumulative incidence over 20 years, while the contralateral breast cancer risk in the bilateral mastectomy group was far lower, at 0.3%; (2) the patients treated with bilateral mastectomy for unilateral breast cancer experienced similar mortality rates as those treated with unilateral surgery; and (3) women who developed a contralateral breast cancer experienced a 4-fold increased hazard of death when compared to women who did not develop a contralateral breast cancer.
Based on the results of this cohort study, women with unilateral breast cancer should be advised that although a bilateral mastectomy greatly diminishes their risk of a contralateral breast cancer, they would, however, experience similar mortality rates as patients treated with lumpectomy or unilateral mastectomy.
