Abstract ES4-1: Which patients can safely avoid radiation after breast conserving surgery?

Abstract

Abstract Whether or not there is a subgroup of patients from whom adjuvant RT can be safely omitted after breast conserving surgery (BCS) for invasive breast cancer (IBC) remains controversial. The Oxford overview (1) shows that whole breast RT (WBRT) after BCS for IBC halves the risk of first recurrence. However the absolute reduction in ipsilateral breast tumour recurrence (IBTR) in ER+ older patients is modest.Guidelines on the omission of RT after BCS vary. The issue is complicated by falling IBTR rates after BCS, adjuvant endocrine therapy (AET) and RT, now around 2-3% at 5 years. The CALGB 9343 trial in women with T1, ER+ tumours receiving tamoxifen and randomized to WBRT or not showed a 3% reduction in local recurrence at 5 years from RT (1% vs 4%,p=<0.001) [2] At a median follow up of 10.5 years the difference in local recurrence had widened in favour of RT (2% RT+, 9% RT-)[3].The PRIME 2 trial randomised 1326 patients with T1-T2 (up to 3cm), pNO, hormone receptor positive tumours =/>65 years after BCS and AET to WBRT or no WBRT. It showed a 2.8% reduction in IBTR from RT (4.1% vs 1.3%,p=0.002) at a median follow up of 5 years(4). An unplanned subgroup analysis by ER status showed a 2.1% reduction in local recurrence (1.2% RT+, 3.3% RT-) from RT but should be interpreted cautiously. However omission of WBRT might be discussed with such patients as an option. Modest absolute improvements in local control from WBRT have to be balanced against increased rates of major coronary events (5).The risk of IBTR is influenced by local therapy, systemic therapy and biology (6).To refine selection of low risk patients, molecular markers of low risk are needed. If molecular signatures of radiosensitivity for breast cancer (7) can be validated from mature RCTs of BCS +/RT, selection of patients cured by surgery and adjuvant endocrine therapy alone could be strengthened.