508 Background: Alterations in the PI3K/AKT/mTOR pathway have been implicated in resistance to trastuzumab (T) in HER2+ breast cancer. BEZ235, a potent oral dual PI3K/mTORC1/2 inhibitor, has demonstrated growth inhibition and apoptosis in HER2+ breast cancer models, including those harboring PI3K pathway alterations, and with T resistance. In a Phase I study, BEZ235 was well tolerated as a single agent in pts with advanced solid tumors. The aim of this study was to determine the MTD of BEZ235 in combination with T in pts with T-resistant HER2+ metastatic breast cancer (mBC) with alterations of the PI3K pathway. Methods: Pts with T-resistant HER2+ mBC (i.e. disease progression during adjuvant therapy or metastatic disease on therapy with T) received oral BEZ235 daily, with weekly T (2 mg/kg). Pts were eligible for enrollment if a tumor sample was demonstrated to contain a molecular alteration of PIK3CA and/or PTEN. Dose escalation was guided by a Bayesian logistic regression model with overdose control. Results: As of 23 Sep 2011, 15 of the 19 enrolled pts were evaluable for dose escalation analysis. BEZ235 was evaluated at 3 dose levels: (1) 400 mg/day (3 pts); (2) 600 mg/day (6 pts); (3) 800 mg/day (10 pts), administered either in capsule form (400 mg) or in sachet form (600 mg and 800 mg). The MTD of BEZ235 in combination with T was estimated to be 600 mg/day. Observed DLTs were G3 nausea at 600 mg/day (1 pt), and G3 nausea, G3 fatigue and G3 skin rash (1 pt each) at 800 mg/day. The most frequent G3/4 adverse events (CTCAE v3.0) suspected to be related to study treatment were diarrhea (4 pts) and nausea (2 pts). No deaths related to study treatment occurred. 1 pt with lung and brain metastases had a partial response. 4 pts had disease stabilization for ≥4 cycles (16 weeks), including 1 pt with liver metastases, in whom BEZ235/T treatment resulted in disease stabilization for more than 21 cycles (84 weeks). Conclusions: BEZ235in combination with T demonstrated an acceptable safety profile in pts with HER2+ mBC and PI3K pathway alterations. Following the Bayesian model recommendation, the MTD for BEZ235 in combination with T was estimated to be 600 mg/day. The safety expansion arm is ongoing at the MTD.
A phase I dose-escalation study of eribulin and S-1 for metastatic breast cancer
