In a Swedish cohort study reported in JAMA Surgery, de Boniface et al found that breast-conserving surgery plus radiation therapy for women with breast cancer was associated with better survival vs mastectomy with or without radiotherapy in analysis adjusting for comorbidities and socioeconomic status.
As stated by the investigators, “Cohort studies show better survival after breast-conserving therapy with postoperative radiotherapy than after mastectomy without radiotherapy. It remains unclear whether this is an independent effect or a consequence of selection bias…. [The objective of this analysis was] to determine whether the reported survival benefit of breast conservation is eliminated by adjustment for two pivotal confounders, comorbidity and socioeconomic status.”
The study used prospectively collected national data on a total of 48,986 women diagnosed with primary invasive T1-2 N0-2 breast cancer who underwent breast surgery in Sweden from 2008 to 2017. The primary outcome measures were overall survival and breast cancer–specific survival.
Despite adjustment for previously unmeasured confounders, breast-conserving surgery plus radiotherapy yielded better survival than mastectomy irrespective of radiotherapy. If both interventions are valid options, mastectomy should not be regarded as equal to breast conservation.— de Boniface et al
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Median follow-up was 6.28 years (range = 0.01–11.70 years). Among the 48,986 women, 29,367 (59.9%) underwent breast-conserving surgery and received radiotherapy; 12,413 (25.3%) underwent mastectomy without radiotherapy; and 7,206 (14.7%) underwent mastectomy and did not receive radiotherapy.
In the entire cohort, all-cause death occurred in 6,573 patients, and death due to breast cancer occurred in 2,313. At 5 years, overall survival was 91.1% (95% confidence interval [CI] = 90.8%–91.3%) and breast cancer–specific survival was 96.3% (95% CI = 96.1%–96.4%).
Unadjusted 5-year overall survival rates were 95.1% in the breast-conserving surgery plus radiotherapy group, 84.5% in the mastectomy without radiotherapy group, and 86.0% in the mastectomy plus radiotherapy group. Corresponding figures for breast cancer–specific survival were 98.2%, 95.0%, and 90.5%.
Compared with women receiving breast-conserving surgery plus radiotherapy, those receiving mastectomy without radiotherapy were older and had a lower level of education and lower income. Both mastectomy groups had a higher comorbidity burden.
In analysis adjusting for tumor characteristics, treatment, socioeconomic status, and Charlson comorbidity index, hazard ratios compared with breast-conserving surgery plus radiotherapy were 1.79 (95% CI = 1.66–1.92) for all-cause mortality and 1.66 (95% CI = 1.45–1.90) for breast cancer–specific mortality in the mastectomy without radiotherapy group and 1.24 (95% CI = 1.13–1.37) and 1.26 (95% CI = 1.08–1.46), respectively, in the mastectomy plus radiotherapy group.
The investigators concluded, “Despite adjustment for previously unmeasured confounders, breast-conserving surgery plus radiotherapy yielded better survival than mastectomy irrespective of radiotherapy. If both interventions are valid options, mastectomy should not be regarded as equal to breast conservation.”
Jana de Boniface, PhD, of the Department of Surgery, Breast Center, Capio St. Göran’s Hospital, Stockholm, is the corresponding author for the JAMA Surgery article.
Disclosure: The study was funded by the Swedish Breast Cancer Association. For full disclosures of the study authors, visit jamanetwork.com.The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.