Phase 2 randomized double blinded placebo control. Approximately 92 patients will be randomized 1:1 to receive the RP2D of PF-04136309 in combination with nab-paclitaxel + gemcitabine (ARM A; n=46) versus nab-paclitaxel + gemcitabine + placebo (ARM B; n=46). The primary objective will be the enhancement of efficacy in terms of PFS.