SAN ANTONIO -- Among patients with early-stage breast cancer, those who received breast- conserving surgery plus radiation therapy had improved overall survival after 10 years compared with those who received mastectomy without radiation therapy, according to data presented at the 2015 San Antonio Breast Cancer Symposium, held Dec. 8-12.
"Comparision of survival outcomes after breast-conserving therapy [breast-conserving surgery followed by radiation therapy(BCT)] versus mastectomy without radiation therapy could provide important information to help support the shared decision-making process and improve the quality of breast cancer care," said Sabine Siesling, PhD, senior researcher at the Netherlands Comprehensive Cancer Organisation, Utrecht, the Netherlands, and professor at the University of Twente, Enschede, the Netherlands.
Several observational studies have provided evidence to suggest that BCT confers better survival than mastectomy; however, these observational studies have limitations, Siesling explained. "Most of these observational studies only followed patients for a maximum of five years. Since recurrences are described to occur after five years as well, getting more insight into the long-term outcomes after different types of surgery based on daily practice experience on a national level is of great importance," she added.
To determine whether there was a difference in the overall survival (OS) and disease-free survival (DFS) outcomes following BCT and mastectomy, Siesling and colleagues used data in the Netherlands Cancer Registry. Data from 37,207 women diagnosed with early-stage breast cancer between 2000 and 2004 was used to estimate 10-year OS, and data from a subcohort of 7,552 patients with similar characteristics diagnosed in 2003 was used to estimate 10-year DFS.
About 58 percent and 62 percent of the patients from the total cohort and subcohort, respectively, received BCT, and the rest of them received mastectomy.
Patients from the total cohort who received BCT had a 10-year OS of 76.8 percent, versus 59.7 percent for those who received mastectomy. Patients from the subcohort who received BCT had a 10-year DFS of 83.6 percent, versus 81.5 percent for those who received mastectomy.
After adjusting for confounding factors, the researchers found that those who received BCT were estimated to be 21 percent more likely to be alive after 10 years than those who received mastectomy. Adjusting for confounding factors also showed that there was no significant difference in DFS between those receiving BCT and those receiving mastectomy. The results were similar in all subgroup analyses, including tumor stage and lymph nodal status.
Analyses of data from the subcohort also showed that the patients who received BCT developed regional recurrences and distant metastases less often than those who received mastectomy. Additional analyses, determining the 10-year distant metastasis-free survival (DMFS), revealed that patients with T1N0 stage breast cancer [small tumors up to 2 cm, with no nodal involvement] who received BCT had a significantly improved 10-year DMFS compared to those who received 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," Siesling said. "We suggest that BCT should be the treatment of choice, especially in T1N0 stage breast cancer when it is medically feasible and according to the patient's wish," she added.
Siesling cautioned that observational studies are prone to confounding by indication. In this study, patients receiving BCT were younger and had more favorable tumor characteristics compared to patients receiving mastectomy. "We corrected for all of these factors in the multivariable analyses; however, we cannot completely rule out this phenomenon," she said. "In addition, residual confounding caused by non-measured factors could also have altered the results. However, we do not expect these factors to overrule the large impact of all variables we included in the analyses," she added.
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Siesling declares no conflicts of interest.
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Abstract: S3-05
Title: Higher 10-year overall survival after breast conserving therapy compared to mastectomy in early stage breast cancer: A population-based study with 37,207 patients
Authors: Marissa C van Maaren1, Linda de Munck1, Geertruida H de Bock2, Jan J Jobsen3, Thijs van Dalen4, Philip Poortmans5, Sabine C Linn6, Luc J A Strobbe7 and Sabine Siesling1,8. 1Netherlands Comprehensive Cancer Organisation, Utrecht, Netherlands; 2University of Groningen, University Medical Center Groningen, Groningen, Netherlands; 3Medical Spectrum Twente, Enschede, Netherlands; 4Diakonessenhuis Utrecht, Utrecht, Netherlands; 5Radboud University Medical Center., Nijmegen, Netherlands; 6Netherlands Cancer Institute, Amsterdam, Netherlands; 7Canisius Wilhelmina Hospital, Nijmegen, Netherlands and 8MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, Netherlands.
Body:
Background: Randomised controlled trials have shown that breast conserving therapy (conserving surgery with radiation therapy, BCT) has equal overall survival (OS) rates as mastectomy without radiation therapy (MAST) in early stage breast cancer. However, 10-year disease-free survival (DFS) in a population-based study was not investigated before. The aim of this study was to compare 10-year OS and DFS after BCT with MAST in Dutch women with early stage breast cancer. Methods: Data of all women diagnosed with primary invasive T1-2N0-1M0 stage breast cancer between 1 January 2000 and 31 December 2004, treated with either BCT or MAST, were selected from the Netherlands Cancer Registry. Multivariable Cox proportional hazard analysis was performed to estimate 10-year OS, stratified for T and N stage. Ten-year DFS was determined in a subgroup of patients diagnosed in 2003, of which an active follow-up was conducted registering all recurrent events within 10 years. Multiple imputation was performed to account for missing data.
Results: Of in total 37,207 patients, 21,734 patients (58.4%) received BCT and 15,473 patients (41.6%) received MAST. The subcohort of 2003 consisted of 7,552 patients, with similar distributions of treatments and characteristics. In the total cohort, 10-year OS was 76.8% (99% CI: 76.1-77.5%) after BCT and 59.7 (99% CI: 58.7-60.7%) after MAST. After correction for confounding, 10-year OS was better after BCT than after MAST (HRadjusted: 0.79 [99% CI 0.75-0.83]). In the 2003 cohort, 10-year DFS was 83.6% (99% CI: 82.5-84.7%) after BCT and 81.5% (99% CI: 79.6-83.4%) after MAST. After correction for confounding, 10-year DFS was comparable for both treatments (HRadjusted 0.91 [99% CI 0.77-1.07]). All results were similar for all subgroups (Table). In the 2003 cohort, 11.0% of the patients experienced distant metastases (DM) after BCT compared to 14.7% after MAST (p<0.001). Regional recurrences (RR) were diagnosed in 2.1% of patients treated with BCT and in 4.0% of patients treated with MAST (p<0.001). Percentages of local recurrences (LR) did not differ between the treatment groups.
Conclusion: BCT showed substantially improved OS compared to MAST. However, while DFS was similar, patients treated with BCT less often developed RR and DM. Although residual factors might explain part of the difference in recurrences, we hypothesise that radiation therapy might largely be responsible for better OS by eliminating residual tumour cells.
Table. Adjusted hazard ratios of breast-conserving surgery with radiation therapy vs. mastectomy on 10-year overall and disease-free survival in T1-2N0-1 staged breast cancer patients n 10-year OS [99% CI] 10-year DFS [99% CI]
n 10-year OS [99% CI] 10-year DFS [99% CI]
Overall cohort
MAST 15,473 1 1
BCT 21,734 0.79 [0.75-0.83] 0.91 [0.79-1.07]
Subgroups
T1N0
MAST 6,092 1 1
BCT 18,860 0.80 [0.74-0.87] 0.81 [0.62-1.08]
T1N1
MAST 2,185 1 1
BCT 3,741 0.80 [0.69-0.92] 1.02 [0.64-1.63]
T2N0
MAST 4,174 1 1
BCT 3,165 0.79 [0.70-0.88] 0.99 [0.72-1.35]
T2N1
MAST 3,022 1 1
BCT 2,060 0.77 [0.67-0.88] 0.82 [0.58-1.15]
All hazard ratios are adjusted for all relevant confounders. Abbreviations: MAST = mastectomy; BCT = breast conserving surgery with post-operative radiation therapy; OS = overall survival; DFS = disease-free survival
This research will be presented at a press conference at the 2015 San Antonio Breast Cancer Symposium, moderated by SABCS Co-director and AACR Past-president Carlos L. Arteaga, MD, director of the Breast Cancer Program at Vanderbilt-Ingram Cancer Center, Thursday, Dec. 10, 7:30 a.m. CT in Room 217D of the Henry B. Gonzalez Convention Center. Reporters who cannot attend the press conference in person can call in using the following information:
- United States/Canada (toll-free): 866-297-6395
- International (toll): 1-847-944-7317
- Conference code number: 41320576
To interview Sabine Siesling, contact Julia Gunther at julia.gunther@aacr.org or 267-250-5441.