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Breast-Conserving Therapy Shows Survival Benefit Compared With Mastectomy in Early-Stage Patients

Findings defy conventional paradigm

When factoring in what is now known about breast cancer biology and heterogeneity, breast-conserving therapy (BCT) may offer a greater survival benefit over mastectomy to women with early-stage, hormone receptor (HR)-positive disease, according to researchers at the University of Texas MD Anderson Cancer Center.

The study findings defy the conventional belief that the two treatment interventions offer equal survival, and show the need to revisit some standards of breast cancer practice in the modern era.

The new research was presented at the 2014 Breast Cancer Symposium, held September 4–6 in San Francisco, California.

In the 1980s, both U.S.-based and international randomized clinical studies found that BCT and mastectomy offered women with early-stage breast cancer equal survival benefits. However, those findings came from a period when little was understood about the biology of breast cancer, explains senior author Isabelle Bedrosian, MD.

“Forty years ago, very little was known about breast cancer disease biology — such as subtypes, differences in radio-sensitivities, radio-resistances, local recurrence, and metastatic potential,” she says. “Since then, there’s been a whole body of biology that’s been learned — none of which has been incorporated into patient survival outcomes for women undergoing BCT or a mastectomy.”

“We thought it was important to visit the issue of BCT versus mastectomy by tumor biology,” she adds.

The researchers hypothesized that they would find that the patient’s surgical choice would matter and would affect survival when tumor biology was considered.

For the retrospective, population-based study, the authors used the National Cancer Database, a nationwide outcomes registry of the American College of Surgeons, the American Cancer Society, and the Commission on Cancer that captures approximately 70% of newly diagnosed cases of cancer in the country. They identified 16,646 women in 2004–2005 with stage I breast cancer who had undergone mastectomy, breast-conserving surgery followed by 6 weeks of radiation (BCT), or breast-conserving surgery without radiation (BCS).

Since estrogen receptor (ER) and progesterone receptor (PR) data were available but the patients’ human epidermal growth factor 2 (HER2) status was not, the researchers categorized the tumors as ER- or PR-positive (HR-positive), or as both ER- and PR-negative (HR-negative). The patients were matched using a broad range of variables, including age, receiving hormone therapy and/or chemotherapy, the type of center where the patients were treated, and co-morbidities.

Of the 16,646 women in the study, 11,214 (67%) received BCT; 3,857 (22%) underwent a mastectomy; and 1,845 (11%) received BCS. Women that received BCT had superior survival compared with those who had a mastectomy or BCS — the 5-year overall survival rates were 96%, 90%, and 87%, respectively. After adjusting for other risk factors, the researchers again found an overall survival benefit for BCT compared with BCS and mastectomy. In a matched cohort of 1,706 patients in each arm, the researchers still found an overall survival benefit with BCT compared with mastectomy in the HR-positive subset but not in the HR-negative subset.

While the new findings are provocative, Bedrosian cautions that they are not practice-changing, as the study was retrospective. Still, the research complements other recent studies that showed that BCT was associated with a survival benefit compared with mastectomy. Also, Bedrosian points to the delivery of radiation therapy as the possible driver of the overall survival benefit.

“We’ve historically considered surgery and radiation therapy as tools to improve local control,” she says. “Yet recent studies suggest that there are survival-related benefits to radiation in excess of local control benefits. Therefore, radiation may be doing something beyond just helping with local control. Also, we know hormone receptive positive tumors are much more sensitive to radiation, which could explain why we found the survival benefit in this group of patients.”

“While retrospective, I think our findings should give the breast cancer community pause. In the future, we may need to reconsider the paradigm that BCT and mastectomy are equivalent,” Bedrosian adds. “When factoring in what we know about tumor biology, that paradigm may no longer hold true.”

Source: MD Anderson Cancer Center; September 4, 2014.

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