Nonmyeloid

Nonmyeloid is a term used in hematology and pathology to describe cells, lineages, or diseases that do not arise from the myeloid branch of hematopoiesis. In normal hematopoietic development, hematopoietic stem cells differentiate into myeloid and lymphoid progenitors. The myeloid lineage gives rise to red blood cells, platelets, granulocytes, and monocytes; the lymphoid lineage gives rise to B cells, T cells, and natural killer cells, among others. Nonmyeloid typically refers to the lymphoid-derived cells and related neoplasms, or more broadly to tissues or cells not derived from myeloid precursors.

In clinical practice, the term is used to distinguish myeloid neoplasms such as acute myeloid leukemia and myelodysplastic syndromes from nonmyeloid (often lymphoid) neoplasms such as acute lymphoblastic leukemia, chronic lymphocytic leukemia, lymphomas, and plasma cell disorders like multiple myeloma. It can appear in differential counts or in diagnoses where lineage origin influences treatment and prognosis.

However, the boundary is not absolute. Some dendritic cells and other immune cells blur the line between lineages, and modern classifications increasingly prefer lineage-specific terms such as lymphoid or myeloid rather than the umbrella nonmyeloid. The term remains encountered in older literature and in certain diagnostic frameworks.

See also: myeloid, lymphoid, leukemia, lymphoma, hematopoiesis.