The phase 2 portion will be implemented with the maximum established tolerated dose (MTD) of XB2001. The target enrollment in the phase 2 portion is 60 patients which will be randomized on a 1:1 basis to XB2001 plus ONIVYDE + LV + 5-FU (Arm 1) or placebo plus ONIVYDE + LV + 5-FU (Arm 2).