In this study we attempt to access nonlinear mechanical properties of tumors by applying external loads. Experiments were performed on subcutaneous tumors implanted in mice. MR elastography acquisitions were realized at 600 Hz while deformations were applied, in order to obtain apparent elasticity (G’) values for each strain application. Results showed nonlinear G’ values increasing with loads, when deformations were clearly observed. Some results showed a decrease of G' potentially due to wave displacement polarization. We showed the feasibility of assessing the nonlinear regime of tumor mechanical properties that may potentially be an indicator of internal tumor forces.