Abstract 859: Regulation of cell cycle and NAD biosynthesis II pathways are associated with differential response to preoperative radiotherapy in locally advanced breast carcinoma

Human breast carcinomas have heterogeneous pathologies, molecular profiles and different responses to therapy. For non-inflammatory locally-advanced breast cancer patients (LABC), preoperative radiotherapy (pRT) is currently indicated after neoadjuvant chemoherapy (CHT), if there is no response to CHT. However, there are no predictive markers of response to pRT in routine clinical practice. Furthermore, understanding of the molecular mechanisms associated to radiotherapy response could open new avenues for overcoming radio-resistance in these patients. In this retrospective study, we have analyzed genes associated with different response to pRT in a neo-adjuvant setting in LABC patients treated with preoperative RT with a total dose of 45 Gy in 15 fractions every second day to the breast and regional lymph nodes, without previous or concomitant systemic therapy. Radical mastectomy was performed 6 weeks after pRT, and adjuvant systemic therapy was administered as per protocol. Response to pRT was classified as pathological complete response (pCR) if there is no evidence of tumor in the breast after mastectomy, partial response (PR) if regression of tumor was >30%, and no response if regression was