There is none. No women with DCIS have been included in a randomized controlled trial.
Cosmetic outcomes are unclear; Second operations to fix the cosmetic outcome may be needed, but reasonable estimates for harm and complications do not exist as bilateral mastectomy has not been systematically studied in DCIS. A paper in Annals of Surgery found that out of 600 women at one institution, 42% of 209 women undergoing bilateral mastectomy had complications versus 29% of 391 women undergoing unilateral mastectomy (42-29% = 13%, added harm). Serious complications of bilateral mastectomy occurred in 14%; 4% with unilateral(14-4% = 10%, added harm).
There is no trade-off between benefit and harm. Since there is no benefit, only harm is possible. Informed medical-decision-making requires a trade-off between added benefit and added harm. This is not the case for DCIS and bilateral mastectomy.
In the last 6 months I have been asked by 3 women diagnosed with DCIS if they should have bilateral mastectomy. Some women had seen up to 3 cancer surgeons and 3 cosmetic surgeons and had been advised by all that bilateral mastectomy was a reasonable option for treatment.
Ductal Carcinoma in Situ (DCIS) is a specific type of breast cancer diagnosis. It used to be uncommon, but since the introduction of screening mammography, nearly 1 in 5 women with cancer are diagnosed with this type. DCIS is not an invasive type of cancer and a woman diagnosed with DCIS will have a low recurrence rate of either local or distantly spread cancer (only 1-2% in a life time). Hence, life expectancy with DCIS is nearly normal.
Two main options for treating DCIS have been studied. First, unilateral (one breast only) mastectomy is the most studied option. In this option, the entire breast is removed. Second, conservative treatment, removing only the area of the cancer rather than the entire breast, followed by radiation therapy, is an alternative despite the fact that this conservative approach has not been studied head to head with mastectomy for DCIS.
Hence, bilateral mastectomy for DCIS has never been studied. Bilateral mastectomy has been limited to women with high risk cancers, such as those with genetic abnormalities like BRCA 1,2. Even in those situations, randomized trials are lacking. Hence, the evidence for/against bilateral mastectomy is based on observational studies. Observational studies are not experiments. In these study designs, some women choose to undergo the procedure while others do not, and we are unclear why. It may be that women who chose to have a bilateral mastectomy are different types of women than those who do not. Hence, a woman’s personal characteristics may obscure our ability to assess the independent effects of treatments examined only in observational studies. For reasons that we will explore in other blog posts, only information from randomized experiments should be used for making your medical decisions. This stringency about the quality of information for making medical-decisions is mine, but through our blogs you will see examples of more people harmed than helped when acting on treatments proposed from observational studies. These examples will support the idea of making decisions only with randomized experiments.
At present, if you have DCIS, a recommendation by a physician for bilateral mastectomy is based on conjecture. Despite the lack of evidence for benefit, bilateral mastectomy for early stage cancer is on the rise. [http://www.ncbi.nlm.nih.gov/pubmed/25182099]. In 1998 2% of women in California underwent bilateral mastectomy; in 2011, 12% did. While some women have stated that removing both breasts reduces their worry of breast cancer in the future, this statement cannot be made based on evidence. We don’t know if women will be better off with bilateral mastectomy so we don’t know if you can/should worry less or not.
Rob McNutt, MD is a contributing editor to THCB.