Study details and key findings

For the study, researchers used data from the National Cancer Institute's SEER Program registry database to evaluate survival outcomes of women who were diagnosed with unilateral stage 0 to III breast cancer from 2000 and 2019.

In total, there were 661,270 women included in the study, with a mean age of 58.7 years. The women were also divided into three groups based on their surgical approach: lumpectomy, a single mastectomy, and a double mastectomy. There were 36,028 women in each of the three groups.

Overall, researchers found that contralateral breast cancers occurred in around 2% of the patients who received either a lumpectomy or a single mastectomy, compared to 0.3% in those who had a double mastectomy.

According to the researchers, patients who experienced contralateral breast cancer saw their risk of breast cancer mortality increase four-fold. At 15 years, the cumulative breast cancer mortality rate was 32.1% for patients who developed contralateral cancer and 14.5% for those who did not.

However, the researchers found that there was not a significant difference in mortality rates at 20 years across the three groups. Among patients who received a single mastectomy, 9.1% had died of breast cancer at 20 years. In comparison, 8.5% had died in the lumpectomy and double mastectomy groups.

"The findings of this cohort study indicate that women with unilateral breast cancer should be advised that bilateral mastectomy greatly reduces the risk of a second cancer, but does not affect mortality," the researchers wrote. However, the researchers noted that the findings may not apply to those with the BRCA gene, which puts them at a higher risk of contralateral breast cancer.

Commentary

According to Steven Narod, a breast cancer researcher and physician at Women's College Hospital in Toronto and the study's lead author, the findings seem "like a paradox" since "[i]f you get a contralateral breast cancer, your risk of dying goes up. But preventing it doesn't improve your survival."

In an accompanying editorial, Seema Ashan Khan and Masha Kocherginsky, both from Northwestern University Feinberg School of Medicine, agreed, saying that the issue of contralateral breast cancers is a "complex biological conundrum."

Currently, there are several potential explanations for why women with contralateral cancers have an increased risk of mortality but still have the same survival rates as others without contralateral cancers. For example, mastectomies may not lower the risk of metastatic recurrence. A local recurrence may signal that there is a problem with the initial tumor, such as the initial treatment failing and leaving microscopic metastases behind.

"A signal that something is going on systemically," Narod said. "That the lung, liver, brain, and bones may also be affected."

In general, more research is needed to understand contralateral breast cancers, how breast cancer spreads, and what can be done to prevent metastatic recurrence in breast cancer survivors.

Although double mastectomies may not improve survival rates for breast cancer patients, many will still choose to have one for several reasons, including avoiding the anxiety of screening and additional tests or trying to avoid cancer treatment again if a new cancer occurs in the second breast.

"That is why chemotherapy and hormonal therapies are so important," said Angela DeMichele, a professor of medicine and coleader of the breast cancer program at the University of Pennsylvania. "They are designed to kill these cells."

Overall, Khan said that the decisions breast cancer patients make about their treatment are complex. "I have always advised women that a second cancer may occur in the future," she said. "But if it occurs there is still a good chance of survival."

Advisory Board's oncology resources

For more insights on oncology, check out these Advisory Board resources:

Growth in demand and costs, as well new technologies and disruptors, will change how cancer care is delivered, experienced, and paid for going forward. This resource outlines four predictions for how the cancer care delivery landscape will evolve by 2030.

Separately, this expert insight explains three strategies organizations can use to leverage oncology pharmacists and improve cancer care. Similarly, these ready-to-use slides outline the major structural shifts impacting cancer care, as well as the strategic decisions that oncology leaders will need to make.

You can search through our oncology topic to see more related resources, including service line outlooks, case studies, and more. (HealthDay/U.S. News & World Report, 7/26; Kolata, New York Times, 7/25; Etienne, People, 7/26; Chen, STAT, 7/25; Bassett, MedPage Today, 7/29)