MTOR and acute myeloid leukemia: Several groups have demonstrated the feasibility of combining cytotoxic chemotherapy and mTORC1 inhibition in relapsed/refractory AML and ALL, and our group has explored whether sirolimus-induced mTOR inhibition, as measured by flow cytometric analysis of S6 ribosomal protein phosphorylation in peripheral blood blasts, predicts response to such regimens [15,16,17,18,19,20,21].