This is a randomized, open-label, multi-center, phase III study of Napabucasin plus bi-weekly FOLFIRI (Arm 1) vs. Napabucasin (Arm 2) for adult patients with metastatic CRC who have failed standard chemotherapy regimens. For patients who have failed bevacizumab with irinotecan-based chemotherapies (treatment failure is defined as radiologic progression of disease during or within 3 months following the last dose), bevacizumab maybe administered in combination with FOLFIRI to patients randomized to Arm 1.