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New research findings question long-held beliefs about breast cancer treatment

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New research from the University of Texas MD Anderson Cancer Center (TX, USA) suggests that breast conserving therapy (BCT) may offer a greater survival benefit than mastectomy, contrary to the conventional belief that the two treatments offer equal survival. The researchers suggest that the research highlights the need to revisit standard breast cancer treatment.

One of the study’s authors Isabelle Bedrosian (MD Anderson) explained that although in the 1980s randomized clinical studies demonstrated that BCT and mastectomy offered women with early-stage breast cancer equal survival benefit, this was a time when little was understood about breast cancer biology.

Bedrosian commented that: “Forty years ago, very little was known about breast cancer disease biology – such as subtypes, differences in radio-sensitivities, radio-resistances, local recurrence and in metastatic potential. 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,”

In the study, the team hypothesized that they would find that patients’ surgical choice would matter and impact survival with tumor biology considered.

The study was a retrospective population-based study in which the researchers used the National Cancer Database (NCDB), which captures approximately 70% of newly diagnosed cases of cancer in the USA.

The team identified 16,646 women in 2004–2005 with stage I disease, all of whom underwent mastectomy, breast-conserving surgery followed by six weeks of radiation (BCT), or breast-conserving surgery without radiation (BCS). The study focused solely on women with stage I disease in order to keep the study group homogenous and because few would be ineligible for BCT.

Because estrogen receptor (ER) and progesterone receptor (PR) data were available and HER2 status was not, the researchers categorized the tumors as ER or PR positive (HR positive), or both ER and PR negative (HR negative). Patients were matched using propensity-score for a broad range of variables; including age, receiving hormone therapy and/or chemotherapy, as well as type of center where patients were treated and comorbidities.

In the study, 11% of the participants received BCS, 67% received BCT and 22% underwent a mastectomy. Women who had BCT had superior survival to those who had a mastectomy or BCS – 5-year overall survival was 96%, 90% and 87% respectively.

After adjusting for other risk factors, the researchers observed an overall survival benefit for BCT compared to BCS and mastectomy. In a matched cohort of 1706 patients in each arm, the researchers still found an overall survival benefit with BCT over mastectomy in the HR-positive subset, however this was not reflected in the HR-negative subset.

While provocative, Bedrosian is quick to highlight that the findings are not practice changing, as the study is retrospective. However, it is important to note that the research complements other recent studies that demonstrated that BCT was associated with a survival benefit when compared with mastectomy. Additionally, 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,” noted Bedrosian. “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.”

Looking forward, Bedrosian and her team hope to use the randomized controlled trial findings from the 1980s, matching those cohorts to current NCDB patients to see if a similar survival benefit could be observed.

“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. When factoring in what we know about tumor biology, that paradigm may no longer hold true.”

Source: MD Anderson Cancer Center press release

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