Breast cancer dormancy is an underlying challenge toward targeting and controlling metastatic recurrence and disease progression. Development of engineered, well-defined in vitro models is necessary to systematically recapitulate tumor dormancy and investigate potential therapeutic strategies. Toward this end, a set of sixteen hydrogel formulations with varying degrees of adhesivity and crosslink density was developed for encapsulation, three-dimensional (3D) culture, and phenotypic assessment of MDA-MB-231 breast cancer cells. The hydrogel adhesivity was regulated by incorporation of RGDS peptide conjugated to acrylate poly(ethylene glycol) (PEG-RGDS) and the crosslink density by incorporation of N-vinyl pyrrolidinone (NVP). Here, we present data concerning the characterization of hydrogel properties (PEG-RGDS incorporation, hydrogel crosslink density, and hydrogel diffusivity as a function of NVP concentration) and phenotypic metrics (viability, early apoptosis, proliferation, metabolic activity, viable cell density, and morphological features) of encapsulated MDA-MB-231s over 15 days in culture. Interpretation of this data can be found in a research article titled “Tunable Hydrogels for Controlling Phenotypic Cancer Cell States to Model Breast Cancer Dormancy and Reactivation” (Pradhan et al., 2019) .