EGFR and neoplasm: Comparing arms in the interval after development of tumor but before the removal of drug, we observed that unlike the no erlotinib treatment groups described earlier, MSC ipsilateral tumors in mice treated with erlotinib were significantly suppressed compared to the relevant control, suggesting that the upregulation of p-EGFR signaling by MSCs made these tumors more sensitive to erlotinib (Figure 4D and E) without affecting tumor histology (see Figure S4B-E in Additional file 4).