Genomic alterations and radioresistance in breast cancer: an analysis of the ProfiLER protocol.

ABSTRACT

BACKGROUND: Breast cancer (BC) patients with comparable prognostic features have heterogeneous outcomes, party related to a possible radiotherapy resistance leading to local-regional recurrences (LRR). The objective of the present study was to identify predictive molecular biomarkers of LRR of BC. PATIENTS AND METHODS: Genetic profile of 146 BC patients' tumours included in the ProfiLER clinical trial (NC01774409) between 2013 and 2016 were analysed using next-generation-sequencing and comparative-genomic-hybridization tests. Patients and tumour characteristics were retrospectively collected and analysed for association with genomic rearrangements (mutations, amplification, deletions). Only gene alterations observed in >3% of the tumours were selected. RESULTS: A total of 193 genomic rearrangements were identified, and 16 were observed in >3% of tumours. One was statistically correlated to the risk of local relapse. A median loco-regional progression-free survival (LRPFS) of 23.6 years was reported for PIK3CA mutation carriers (n = 31, 21.2%) versus 9.9 years for PIK3CA wild-type patients (HR 0.27, 95% CI 0.12-0.65, P = 0.002 in univariate analysis). PIK3CA mutation was identified as an independent protective factor on LRR using multivariate analysis (HR 0.29, 95% CI 0.09-0.99, P = 0.047). All other mutations, amplifications or deletions were not found associated with LRPFS. CONCLUSION: PIK3CA mutation was associated with a lower risk of local relapse in this population of BCs. This is consistent with recent studies suggesting PIK3CA to be part of biological pathways impacting the radiosensitivity.