Dr. Vasily Giannakeas is a scientist at the Women’s College Hospital (WCH) Research and Innovation Institute, and Dr. Steven Narod is a senior scientist and director of the Familial Breast Cancer Research Unit at the institute. He is also a professor at the University of Toronto and author of A Fair Trial: The Foundations of Breast Cancer. Dr. David Lim is a surgeon and breast cancer researcher at WCH.
Women with breast cancer in one breast often choose to have both breasts removed – in a procedure known as a bilateral mastectomy – just to be on the safe side. Doctors rarely recommend this operation, except for women with a BRCA1 or BRCA2 genetic mutation, who have a markedly increased risk of developing breast cancer compared with the general population.
The decision to remove both breasts is largely patient-led, but most surgeons in Canada or the U.S. will comply with the patient’s wish.
There are many reasons why a woman will make this decision. For some, the more symmetric result of a double mastectomy, followed by the reconstruction of both breasts, is a factor. But for most patients, the decision to remove both breasts is based on the fear of the cancer coming back. They wish to avoid a second diagnosis, a second surgery and possibly more chemotherapy and radiotherapy. Many patients value the relief provided by reducing the risk of getting a second cancer and are glad to hear that they no longer need to undergo annual mammograms. Foremost is the belief that preventing a second breast cancer in the opposite breast, also known as contralateral breast cancer, will lower the risk of dying from breast cancer. Using a large database of breast cancer patients, we sought to test this theory in order to offer patients the best information possible, and help them in shared decision-making with their health care providers.
Fortunately, the SEER database in the U.S. collects extensive data on patients with breast cancer and makes them freely available to number crunchers like us. In July, we published the paper “Bilateral Mastectomy and Breast Cancer Mortality” in the JAMA Oncology medical journal, and our findings challenge the belief that preventing a second breast cancer in the opposite breast will lower a patient’s risk of dying from breast cancer.
To start we must ask: what is the risk of getting a contralateral breast cancer (a cancer in the second breast)? Over a 20-year span after the diagnosis of the first cancer, the risk of getting cancer in the opposite breast is about 7 per cent. This number does not vary much according to the patient’s age at initial diagnosis and is surprisingly similar for women with very early-stage breast cancer and those with more advanced breast cancer.
Unfortunately, developing a contralateral breast cancer does raise the patient’s chance of dying from breast cancer. In our study, women with breast cancer on one side had a 20-year survival rate of 84 per cent, compared with 68 per cent for those with cancer in both breasts. For patients with ductal carcinoma in situ (or DCIS, which affects the cells of the milk ducts), the survival rate fell from 98 per cent to 87 per cent if a cancer was later diagnosed in the opposite breast.
The good news is that a bilateral mastectomy does prevent a contralateral breast cancer. We found that for those who underwent this procedure, the risk of contralateral breast cancer fell from 7 per cent to less than 1 per cent.
However, we were surprised to find that a bilateral mastectomy does not reduce a patient’s chance of dying from breast cancer. In our study, among 36,028 women who had just a tumour removed, also known as a lumpectomy, there were 3,077 deaths from breast cancer. We took a look at another group of 36,028 closely matched women who chose to have both breasts removed, and found there were 3,062 deaths from breast cancer among them. Our findings suggest that the removal of 36,028 healthy breasts dropped the death toll by only 15, even though there were 669 fewer contralateral breast cancers in the bilateral mastectomy group.
These findings are valuable to the patient and their physician as they look to decide on surgical options to treat breast cancer. However, they also raise several fundamental questions about the nature of breast cancer itself. Before our research, doctors treated a contralateral breast cancer as an independent cancer that behaves much like the first cancer and should be treated as such. Our research suggests otherwise – that a contralateral breast cancer is more likely to be a marker telling us that the first cancer is aggressive – the contralateral cancer signals that the first cancer might have already spread early on, similar to cancer-positive lymph nodes. The more positive lymph nodes at diagnosis, the poorer the survival rate – and removing the lymph nodes does not improve survival.
Our study is part of the puzzle. It also raises many new questions. If preventing contralateral breast cancer doesn’t reduce the risk of death, why would early detection by mammography be any better? Currently, the standard of care is to offer a mammogram every six months to a year after the first cancer appears. To our knowledge, this has not been proven effective. Furthermore, does the second cancer require chemotherapy? About one-third of patients with contralateral breast cancer are treated with chemo. However, it now appears that we are really trying to treat the first cancer, and chemotherapy may not be as effective at this time.
These are compelling questions that we hope to address in future studies. It seems that to make progress in the fight against breast cancer, we have to be able to detect and treat breast cancer cells at the earliest stage possible, even before the first cancer becomes apparent – no small order.