Understanding the role of the tumor microenvironment during cancer progression and metastasis is complicated by interactions between cells, the extracellular matrix (ECM), and a variety of biomolecules. Using a synthetic strategy, we investigated proteolytic modes of migration for HT-1080 fibrosarcoma cells in an environment that limited confounding extracellular influences. A large percentage of HT-1080s migrated through a Rho kinase (ROCK)-dependent rounded morphology with a leading edge protrusion that defined the direction of migration, and migration was only weakly dependent on the adhesive peptide RGDS. HT-1080s migrating in thiol-ene hydrogels are more rounded and exhibit much more invasive behavior than dermal fibroblasts. Our results indicate that HT-1080s have the capacity to migrate through a mechanism that is distinct from mesenchymal cells, with significant amoeboid character even when utilizing a proteolytic migration strategy. The migration mode observed here provides insight into the invasiveness of metastatic cells in vivo and demonstrates the potential of a synthetic strategy for investigating complex biological problems.