Long-Term Outcomes of Radiation Monotherapy Versus Combined Radiation Monotherapy + Hormone Therapy in Low-Risk Early-Stage Breast Cancer Patients 70 Years or Older After Breast-Conserving Surgery.

Abstract

PURPOSE: Standard therapy for breast cancer after breast-conserving surgery is radiation therapy (RT) plus hormone therapy (HT). For patients with a low-risk of recurrence, there is an interest in deescalating therapy. METHODS AND MATERIALS: A retrospective study was carried out for patients treated at the Swedish Cancer Institute from 2000 to 2015, aged 70 years or older, with pT1N0 or pT1NX estrogen receptor-positive and ERBB2-negative unifocal breast cancer without positive surgical margins, high nuclear grade, or lymphovascular invasion. RESULTS: Patient numbers were sufficient to carry out analyses for RT + HT (n = 307) and RT alone (n = 148). The median follow-up was 9.6 years. There were no statistically significant differences in adjusted overall survival (OS), disease-specific death, progression-free survival (PFS), distant recurrence, and second primary cancers with RT monotherapy compared with RT + HT. Cumulative rates of all of these outcomes were <5%, even at 15 years of follow-up, regardless of treatment, greatly outweighed by the incidence of death from other causes in this elderly population. In matched analysis, we calculated a hazard ratio of 1.12 (95% CI, 0.82-1.53) for RT versus RT + HT for OS and a hazard ratio of 1.12 (95% CI, 0.82-1.53) for RT versus RT + HT for PFS. CONCLUSIONS: Our data suggest that elderly, low-risk breast cancer patients have similarly high OS and PFS with low rates of local recurrence, distant recurrence, and death from breast cancer with much higher rates of death from competing causes, whether treated with RT or HT + RT. These patients are likely to die of other causes without disease recurrence, regardless of which of these treatments is used. Thus, they may benefit from the administration of more modern forms of breast irradiation without the need for adjuvant systemic hormone therapy. A detailed analysis of which clinical, pathologic, genomic, and comorbidity variables are needed to select these patients.