Study of Eribulin Mesylate in Combination With PEGylated Recombinant Human Hyaluronidase (PEGPH20) Versus Eribulin Mesylate Alone in Subjects With Human Epidermal Growth Factor Receptor 2 (HER2)-Negative, High-Hyaluronan (HA) Metastatic Breast Cancer (MBC)

Phase 1b will occur in two parts: 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. Part 2 (Phase 1b "Expansion Part"): A total of 12 additional participants will be enrolled at the RP2D determined in Part 1 (using Phase 1b criteria, i.e., participants previously treated with up to 2 lines of systemic anticancer therapy) in order to assess the safety profile of the combination and identify any potential safety signals and the incidence of thromboembolic events in this population (RP2D determined dosing). In Phase 2, participants will be stratified by triple negative breast cancer (TNBC) status and randomized 1:1 to receive eribulin mesylate and PEGPH20 at the established RP2D level or eribulin mesylate alone at 1.4 milligrams per square meters (mg/m\^2).