SAN ANTONIO — Breast-conserving therapy (BCT), which consists of lumpectomy with radiotherapy, might be a better option than mastectomy, according to long-term data from a large retrospective study.
The observational study, involving more than 37,000 women in the Netherlands, provides 10-year data.
The results show that the relative risk for death after 10 years was nearly 20% lower in women who underwent BCT than in those who underwent mastectomy alone (hazard ratio, 0.81; P < .001).
The 10-year rate of overall survival was better with BCT than with mastectomy (76.8% vs 59.7%).
In the BCT group, overall survival benefits extended across tumor size (T1 and T2) and nodal status (N0 and N1).
A slight majority of the women (58.4%) received BCT.
This study, which involved women diagnosed from 2000 to 2004, is important, in part, because it provides 10-year data, said Sabine Siesling, PhD, senior researcher at the Netherlands Comprehensive Cancer Organization in Utrecht.
Most recent observational studies, which have also shown better survival with BCT, have been limited to 5 years of post-treatment data, which is "quite short" for breast cancer, Dr Siesling told reporters during a press briefing here at the San Antonio Breast Cancer Symposium 2015.
"The main take-away message is that breast-conserving therapy should be the treatment of choice, especially in small tumors, when it is medically feasible," she concluded.
An American clinician agrees.
"Breast conservation in the appropriately selected patient is the right thing to do," said Carlos Arteaga, MD, from the Vanderbilt-Ingram Cancer Center in Nashville, Tennessee, who is a director of the symposium.
Nevertheless, Dr Arteaga stated that the study would not likely change current guidelines. Mastectomy is generally recommended when, among other things, tumor multicentricity is present or the size of the tumor (relative to the size of the breast) dictates.
In the Dutch study, the women who underwent BCT tended to be younger and to have smaller well-differentiated ductal tumors, unifocal tumors, less hormonal therapy, and less axillary lymph node dissection.
"We corrected for all of these factors in the multivariable analyses; however, we cannot completely rule out this phenomenon," Dr Siesling said in a press statement.
The team also examined data from a subcohort of 7552 patients with similar characteristics diagnosed specifically in 2003, which was used to estimate 10-year disease-free survival.
In this subcohort, 10-year disease-free survival was better with BCT than with mastectomy, although the difference was not significant (83.6% vs 81.5%).
However, the subcohort data showed that the patients who underwent BCT developed regional recurrences and distant metastases less often than those who underwent mastectomy.
On further analysis of the subcohort data, patients with T1N0 stage breast cancer who underwent BCT were shown to have significantly better 10-year distant metastasis-free survival than those who underwent mastectomy.
"We think that radiation therapy may have played an important role in the difference in the outcomes from both treatments, although we cannot prove it with our data," Dr Siesling said in a press statement.
She also explained that, in the Netherlands, radiation therapy is not performed in conjunction with mastectomy.
The study has limitations, Dr Siesling acknowledged, such as potential confounders that could be at play, including the fact that there was no information about the HER2 status of the patients or their comorbidities.
"However, we do not expect these factors to overrule the large impact of all the variables we included in the analyses," she added.
Dr Siesling and her coauthors have disclosed no relevant financial relationships. Dr Arteaga reports receiving consulting fees from Roche, Monogram (LabCorp), AstraZeneca, Novartis, Genentech, and Susan G. Komen.
San Antonio Breast Cancer Symposium (SABCS) 2015: Abstract S3-05. Presented December 10, 2015.