SOX2 is a critical transcription factor that regulates cancer cell proliferation, migration, invasion, and metastasis45–49, and we showed here that the T47D cell proliferation in a suspension culture and the increase in the amount of the SOX2 protein were cooperatively enhanced by only the combination of nectin-4 and p95-ErbB2, but not by that of nectin-4 and either ErbB2 or ErbB2∆Ex16, and that the T47D cell proliferation in a suspension culture cooperatively enhanced by nectin-4 and p95-ErbB2 was inhibited by the MST1/2 inhibitor or SOX2 knockdown. The gene discussed is MST1; the disease is cancer.