Subset of Patients With Luminal A Breast Cancer May Not Benefit From Radiotherapy
In an analysis reported in the Journal of Clinical Oncology, Liu et al found that a subset of patients with luminal A breast cancer may not need radiotherapy to prevent relapse.
Study Details
The study involved samples from 501 older patients with node-negative disease who were randomized to receive tamoxifen or tamoxifen plus breast radiotherapy. Immunohistochemical analysis of estrogen receptor, progesterone receptor, HER2, cytokeratin 5/6, EGFR, and Ki-67 status was performed, with patients being classified as luminal A (n = 265), luminal B (n = 165), or high-risk subtypes (n = 71; luminal HER2 in 22, HER2-enriched in 13, basal-like in 30, and triple-negative nonbasal in 6). Median follow-up was 10 years.
Relapse Risk
Subtype was prognostic for ipsilateral relapse, with estimated 10-year rates of 5.2% for luminal A, 10.5% for luminal B, and 21.3% for high-risk subtypes (P < .001). Hazard ratios (HRs) for tamoxifen plus radiotherapy vs tamoxifen alone were higher for luminal A (0.40) and luminal B tumors (0.51) than for the high-risk group (0.13), although the subtype by treatment interaction was not significant (P = .26).
Clinical Low-Risk Luminal A
An exploratory analysis showed that the 10-year rate of ipsilateral relapse was 3.1% among 151 women with luminal A tumors who were at clinical low risk (defined as age > 60 years, T1 disease, and grade 1 or 2 disease), compared with 11.8% among 341 women with clinical high risk (P = .0063). Among women with clinical low-risk luminal A disease, the 10-year rate of ipsilateral relapse was 1.3% among those receiving tamoxifen vs 5.0% among those receiving tamoxifen plus radiotherapy (P = .42).
On multivariate analysis, radiotherapy (HR = 0.31, P < .001), clinical risk group (HR = 2.2, P = .025), and luminal A subtype (HR = 0.25, P < .001) were significantly associated with ipsilateral relapse.
The investigators concluded, “Immunohistochemical subtyping was prognostic for [ipsilateral breast relapse] but was not predictive of benefit from [radiotherapy]. Further studies may validate the exploratory finding of a low-risk luminal A group who may be spared breast [radiotherapy].”
Anthony W. Fyles, MD, of Princess Margaret Cancer Centre, is the corresponding author of the Journal of Clinical Oncology article.
The study was supported by the Canadian Institutes of Health Research; the Guglietti Foundation; the Princess Margaret Cancer Foundation; the Campbell Family Institute for Cancer Research; and the Ministry of Health and Long-term Planning, Province of Ontario.
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