Phase 1b (dose-finding cohorts) will be open label as patients will receive ascending doses of PF-04136309 in combination with nab-paclitaxel + gemcitabine. The observation period for dose-limiting toxicities (DLTs) will be from Day 1 to Day 28. Pharmacokinetic (PK) and pharmacodynamic (PD) properties of PF-04136309 will also be assessed. The criteria for dose escalation will be based on a modified toxicity probability interval (mTPI) method. After evaluating the safety and other results (eg, PK) from patients enrolled in the dose escalation cohorts, a dose level will be selected to be further evaluated as the Recommended Phase 2 Dose (RP2D). A minimum of 6 patients, up to 12 patients, will be treated at this dose level to establish it as the RP2D. To further evaluate safety and pharmacodynamics, the number of patients enrolled during this part of the study (Phase 1b) may be N up to 20. The study will stop if all PF-04136309 doses explored appear to be overly toxic.