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Abstract
Background:
Radiotherapy after breast conservation has become the standard of care. Prior meta-analyses on effects of radiotherapy predated availability of gene expression profiling (GEP) to assess recurrence risk and/or did not include all relevant outcomes. This analysis used GEP information with pooled individual-level data to evaluate the impact of omitting radiotherapy on recurrence and mortality.

Methods:
We considered trials that evaluated or administered radiotherapy after lumpectomy in women with low-risk breast cancer. Women included had undergone lumpectomy and were treated with hormonal therapy for stage I, ER+ and/or PR+, HER2- breast cancer with Oncotype scores no greater than 18. Recurrence-free interval (RFI), type of RFI (locoregional or distant), and breast cancer-specific and overall survival were compared between no radiotherapy and radiotherapy using adjusted Cox models. All statistical tests were two-sided.

Results:
The final sample included 1778 women from seven trials. Omission of radiotherapy was associated with an overall adjusted hazard ratio of 2.59 (95% confidence interval [CI] = 1.38 to 4.89, P = .003) for RFI. There was a statistically significant increase in any first locoregional recurrence (P = .001), but not distant recurrence events (P = .90), or breast cancer-specific (P = .85) or overall survival (P = .61). Five-year RFI rate was high (93.5% for no radiotherapy vs 97.9% for radiotherapy; absolute reduction = 4.4%, 95% CI = 0.7% to 8.1%, P = .03). The effects of radiotherapy varied across subgroups, with lower RFI rates for those with Oncotype scores of less than 11 (vs 11-18), older (vs younger), and ER+/PR+ status (vs other).

Conclusions:
Omission of radiotherapy in hormone-sensitive patients with low recurrence risk may lead to a modest increase in locoregional recurrence event rates, but does not appear to increase the rate of distant recurrence or death.

Author information

Jayasekera J1, Schechter CB2, Sparano JA3, Jagsi R4, White J5, Chapman JW6, Whelan T7,8, Anderson SJ9, Fyles AW3, Sauerbrei W10, Zellars RC11, Li Y12, Song J12, Huang X12, Julian TB13, Luta G14, Berry DA12, Feuer EJ15, Mandelblatt J1; CISNET-BOLD Collaborative Group.
1
Department of Oncology, Georgetown University Medical Center and Cancer Prevention and Control Program, Georgetown-Lombardi Comprehensive Cancer Center, Washington, DC.
2
Departments of Family and Social Medicine and Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY.
3
NRG Oncology, and the Department of Biostatistics, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA.
4
Department of Radiation Oncology, University of Michigan, Ann Arbor, MI.
5
The James Department of Radiation Oncology, The Ohio State University Comprehensive Cancer Center, Columbus, OH.
6
Canadian Cancer Trials Group, Queen's University, Kingston, ON, Canada.
7
Research Department of Oncology, Division of Radiation Oncology, McMaster University, Hamilton, ON, Canada.
8
Radiation Medicine Program, Princess Margaret Cancer Centre, Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada.
9
Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY.
10
Institute for Medical Biometry and Statistics, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany.
11
Department of Radiation Oncology, Indiana University, Bloomington, IN.
12
Department of Biostatistics, Division of Quantitative Sciences, The University of Texas MD Anderson Cancer Center, Houston, TX.
13
NRG Oncology, and The Division of Breast Surgical Oncology, Allegheny General Hospital, Allegheny Health Network, Pittsburgh, PA.
14
Department of Biostatistics, Bioinformatics and Biomathematics, Georgetown-Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC.
15
Division of Cancer Control and Population Sciences, National Cancer Institute, Bethesda, MD.