The invention aims to provide a method of screening for a therapeutic drug for cancer as a molecular-targeted drug targeting some protein from a number of candidate target proteins, without identifying the true target protein. In particular, the invention provides a method of screening for a therapeutic drug for cancer, including (i) a step of expressing an exogenous cell regulatory factor in a target cancer cell under contact or no contact with a test substance, (ii) a step of confirming change in the cancer cell, and (iii) a step of selecting the test substance as a therapeutic drug for cancer when the change of cancer cell increased under contact with the test substance as compared to no contact therewith.