Anti-cancer treatment and therapeutic methods are provided in which an antibody that binds specifically to glycosylated PD-L1 relative to unglycosylated PD-L1 and blocks binding of PD-L1 to PD-1 is administered to a subject in need in combination with an antibody that binds specifically to glycosylated PD-L1 relative to unglycosylated PD-L1, blocks binding of PD-L1 to PD-1 and also promotes internalization and degradation of PD-L1. The anti-cancer methods utilize antibodies that recognize specific epitopes on glycosylated PD-L1 protein, as well as antibodies that exhibit the IPD function of both blocking the binding of PD-L1 to PD-1 and also facilitating the internalization of PD-L1 on cells expressing PD-L1. Methods in which such antibody combinations are especially useful include cancer and tumor treatments and therapies in which the cancer or tumor is a PD-L1 positive cancer or tumor.