This is an open label, multi-center, multi-arm, dose-escalation study of BBI608 administered in combination with either Gemcitabine and nab-Paclitaxel, mFOLFIRINOX, FOLFIRI, or MM-398 with 5-FU and leucovorin. A study cycle will consist of daily and continuous oral administration of BBI608 for four weeks (28 days) in combination with Gemcitabine and nab-Paclitaxel, mFOLFIRINOX, FOLFIRI, or MM-398 with 5-FU and leucovorin. Combination treatment will continue in 28 day cycles until disease progression, unacceptable toxicity or another discontinuation criterion is met. BBI608 may be continued post-progression if the patient is obtaining potential clinical benefit, in the opinion of the investigator. If administration of Gemcitabine and/or nab-Paclitaxel, mFOLFIRINOX, FOLFIRI, or MM-398 with 5-FU and leucovorin is discontinued due to chemotherapy backbone-related toxicities, the administration of BBI608 can be continued.