Sabine Siesling, PhD
Women who opt for breast-conserving therapy (BCT) and radiation to treat their early-stage breast cancer are about 20% more likely to be alive after 10 years compared with their counterparts who had mastectomy, according to findings of a large, population-based study carried out in the Netherlands.
For the first time, investigators also looked specifically at 10-year distant metastasis-free survival (DMFS) in this group of women. Although outcomes with BCT and mastectomy were similar, regional recurrences and distant metastases developed less frequently in patients treated with BCT. Additionally, for women with T1N0 breast cancer who chose BCT, 10-year survival was better.
“Breast-conserving therapy should be the treatment of choice, especially in T1N0 breast cancer, when it is medically feasible and according to the patient’s wishes,” said Sabine Siesling, PhD, a senior researcher at the Netherlands Comprehensive Cancer Center Organization and a professor at the University of Twente.
Siesling, who presented the study findings at the 2015 San Antonio Breast Cancer Symposium (SABCS), noted that one of the limitations of previous observational studies that showed a survival advantage with BCT is that patients were only followed for 5 years: “As we all know, 5 years in breast cancer is quite short.”
To address that issue, the study Siesling reported at SABCS compared overall survival (OS) and DMFS over 10 years, using the Netherlands Cancer Registry that includes patients who received treatment across the country’s 90 hospitals.
The total study population (N = 37,207) involved women whose first breast tumor (T1-2N0-1M0) was diagnosed between 2000 and 2004. Of the total cohort, 58.4% had BCT. The DMFS analysis was based on a subset of women (n = 7552) diagnosed in 2003. Investigators used multivariable Cox proportional hazard analyses and stratified the data according to patients’ tumor and nodal stage, and characteristics of patients were similar across both the total and the smaller cohort.
Ten-year OS for the total cohort was 76.8% with BCT versus 59.7% after mastectomy (99% CI, 58.7-60.7). At a median follow-up of 11.3 years, and after adjusting for any confounding variables such as age and receipt of adjuvant therapies, 10-year OS remained better with BCT (HR, 0.81, P
<.001), and for OS “in the different staging subgroups, we saw the same results,” said Siesling.
For the DMFS subset, of the 61.5% of women who had BCT, 11% developed distant metastases after 10 years of follow-up compared with 14.7% in mastectomy group. When researchers examined the tumor and nodal stage subgroups, “we found this result mainly in the T1-N0 subgroup [small tumors up to 2 cm with no nodal involvement],” Siesling said (HR, 0.74, P
The DMFS result, however, was not observed in the other larger tumor subgroups: T1N1 (HR, 1.00; P
= .994), T2N0 (HR, 0.94; P
= .644), and T2N1 (HR, 0.95; P
Siesling hypothesized that the more favorable DMFS results in the T1-N0 subgroup that had BCT may be attributable to radiation therapy. In these women, “the radiotherapy probably destroyed all of the tumor cells left,” thus reducing the risk of distant metastases.
Among the total study cohort, women who chose BCT were younger and had more favorable tumor characteristics compared with patients receiving mastectomy, Siesling said.
“We corrected for all of these factors in the multivariable analyses; however, we cannot completely rule out this phenomenon. In addition, residual confounding caused by other non-measured factors could also have altered the results,” Siesling explained, citing the lack of information on comorbidity and HER2 status as examples. Nevertheless, she said, “we do not expect these factors to overrule the large impact of all variables included in the analysis: the overall survival for breast-conserving therapy compared to mastectomy is better in every T and N stage, and distant metastasis-free survival is mainly better in patients who have tumors smaller than 2 centimeters without lymph node involvement.”
Siesling reiterated, however, ”the decision must fit with the patient herself.” Even with BCT for example, she noted that the surgery may not be nipple-sparing, depending on the location of the tumor, and this can impact a woman’s treatment choice. Another important consideration, especially for women living in rural areas, she said, may be the burden of daily travel for radiation treatments.
Carlos L. Arteaga, MD, associate director of clinical research and leader of the breast cancer program at Vanderbilt-Ingram Cancer Center, who moderated the press conference where the study results were announced, said he did not expect these findings to change current guidelines in the United States: