Dual inhibition of DNA double strand break (DSB) repair and PI3K pathway with BEZ235 (BEZ) to sensitize refractory metastatic (met) triple negative breast cancer (TNBC) to nab paclitaxel/cisplatin (pac/cis) in a patient with an exceptional response (ExRx).

Abstract

156 Background: Whether EGFR is a critical target in met TNBC is unknown. Here we report the clinical history & tumor molecular alterations in a patient with refractory metTNBC who had an ExRx to pac/cis. Methods: Following IRB-approved informed consent, targeted NGS (Foundation Medicine) and WGS (TGEN) was performed on the pt’s FFPE primary TNBC and 2 recurrent lymph nodes to characterize all classes of genomic alterations in cancer-related genes. RPPA was performed at a CLIA-certified laboratory (Theranostics Health) and George Mason Univ where immunostaining was directed against HER1/2/3 pathway and other proteins. Results: At age 58 in 2006, pt had T1c 1+ node TNBC treated with FAC/T. Between 2008 and 2011 she had 4 chemotherapy-refractory recurrences in axilla, supraclavicular (SC), internal mammary (IM) LNs treated unsuccessfully with surgery, radiation and multiple cytotoxic agents including carboplatin. In 2011, following SC LN biopsy, she was treated with BEZ, a PI3K/mTOR, ATM, ATR, DNA-PKcs inhibitor, had a 3 mo response, followed by rapidly enlarging progressive disease (PD) in IM LNs pushing sternum anteriorly. She was treated with pac/cis and had an ongoing complete response (CR) of 2.5+ yrs. NGS of 2011 SC LN (pre-BEZ) & 2012 IM LN (post-BEZ): TP53 & BRCA2 (somatic 15% mutant allele freq) mutations, FOXM1 amplification; SMARCA4 (BRG1) deletion RPPA (GMU) 2011 SC LN (Pre-BEZ): 3+ EGFR; 2+ p-EGFR, p-AKT, p-MEK1/2, p-mTOR RPPA (Theranostics) 2012 IM LN (post-BEZ): 3+ p-MEK1/2 (EGFR & p-EGFR 0) (AR-). Conclusions: Strong EGFR signaling associated with chemo-resistant metTNBC in 2011 SC LN was not present in post-BEZ rapid PD in IM LN which then had durable CR with pac/cis. BEZ inhibits DSB repair, sensitizing cancers to DNA damaging agents (Gil del Alcazar, Clin Ca Res 20:1235, 2014). Progression of p-AKT-activated TNBC following response to inhibitors of PI3K & DNA repair shows DSB repair-deficiency and MAPK activation (Juvekar, Cancer Dis 2:1048, 2012). A prospective trial of BEZ followed at PD by pac/cis in metTNBC is warranted.