The term's literal derivation is "originating from or produced in the marrow". It is applied to leukemias that originate in a marrow stem cell or early marrow progenitor cell, especially acute and chronic myelogenous leukemia. It also distinguishes the myelogenous leukemias, which originate in a cell that is in the blood cell-forming lineages and usually do not affect lymphocytes overtly, from those that originate in a lymphocyte, e.g.acute and chronic lymphocytic leukemia. Myeloid and myelocytic are synonomous terms and the designations acute or chronic myeloid or myelocytic leukemia are used by some but are not the preferred terms.