Part 1: Run-in safety cohort(s) (dose levels 1, 0, and -1, as necessary) of 6 participants each will be conducted until the RP2D is determined. The purpose of the run-in safety cohort(s) is to study the safety of the 2-drug combination and determine a RP2D. Dose limiting toxicity (DLT) will be assessed in the first cycle to determine the RP2D of eribulin mesylate in combination with PEGPH20.