MTOR and plasma cell myeloma: However, in other subsets of tumor like myeloma [6, 13, 14], thyroid carcinoma [15] and breast cancer [16], DEPTOR acts as an oncogene and positively correlates with poor survival of tumor patients, since DEPTOR overexpression simultaneously suppresses S6K1, a downstream molecule of mTOR, and thus relieves the feedback inhibition from mTOR to PI3K, boosting AKT activity for cancer cells survival [14, 15, 17].