The substance P (SP)/neurokinin (NK)-1 receptor system plays an important role in cancer. After binding to the NK-1 receptor, SP induces tumor cell proliferation, migration of tumor cells (invasion, infiltration and metastasis) and angiogenesis. In contrast, NK-1 receptor antagonists inhibit tumor cell proliferation (tumor cells die by apoptosis), block the migratory activity of tumor cells, and exert antiangiogenic properties. The induction of apoptosis offers an appropriate method for cancer treatment. The NK-1 receptor can be considered as a target in cancer treatment. A common mechanism for cancer cell proliferation mediated by SP and the NK-1 receptor occurs and NK-1 receptor antagonists are broad-spectrum antineoplastic drugs. The NK-1 receptor antagonist aprepitant is used in clinical practice and exerts an antitumor action against a large number of different human tumor cells. In the future, such antitumor action should be tested in human clinical trials.