Quantitative phase imaging (QPI) offers a label-free approach to non-invasively characterize cellular processes by exploiting their refractive index based intrinsic contrast. QPI captures this contrast by translating refractive index associated phase shifts into intensity-based quantifiable data with nanoscale sensitivity. It, therefore, provides quantitative characterization of biophysical properties of cells and tissue in their natural states. Here we review QPI research, discuss its potential and identify its challenges in the context of advancing precision cancer medicine.