The longitudinal progression of glioblastoma was monitored in a cohort of mice with MRE and conventional RARE MRI. Increasing tumor size was easily seen with both modalities. In most cases, MRE maps showed a tumor margin that was sharper than RARE. Results were registered with histology, and variation of the shear modulus was compared with histology features. Both MRE and RARE demonstrated tumor regions with varying levels of heterogeneity, and in one animal, both homogeneous and heterogeneous parts were found to be growing separately as sub-populations of the same glioblastoma cell line within the brain.