CD117 (Myeloid Cell Marker)

CD117 (c-KIT) is a receptor tyrosine kinase found on hematopoietic stem/progenitor cells, mast cells, and many myeloid progenitors and AML blasts. It’s commonly included in myeloid panels but is not myeloid-specific, since other cell types (e.g., mast cells, germ cells) also express it. Interpretation requires correlation with additional markers and morphology.

CD117 positive means cells express the CD117 protein (c-KIT), a cell-surface receptor tyrosine kinase. It’s used in pathology to identify certain cell types—commonly mast cells, hematopoietic stem cells, and interstitial cells of Cajal—and helps diagnose tumors like gastrointestinal stromal tumors (GIST). CD117 positivity can indicate c-KIT–driven growth and may influence use of targeted therapies that inhibit this receptor.

CD117 (c‑KIT) is associated with gastrointestinal stromal tumors (GIST), systemic mastocytosis, and activating mutations in some acute myeloid leukemias. It is also expressed or mutated in subsets of melanomas, testicular germ‑cell tumors (seminomas), and occasional breast and lung cancers. CD117 abnormalities guide diagnosis and targeted therapy in several of these conditions.

Yes. CD15 (Lewis X) is commonly used as a myeloid/granulocyte marker. It is strongly expressed on mature neutrophils and other granulocytes, variably on monocytes, and can appear on some non‑myeloid cells. CD15 is useful for identifying myeloid/granulocytic differentiation in flow cytometry and immunohistochemistry but is not absolutely specific and should be interpreted with additional markers.

A myeloid marker is a cell-surface or intracellular antigen expressed by cells of the myeloid lineage (e.g., neutrophils, monocytes, eosinophils). Common markers include CD13, CD33, CD14, CD15 and myeloperoxidase. They are detected by flow cytometry or immunohistochemistry to identify, classify and monitor myeloid disorders such as acute myeloid leukemia and to distinguish myeloid from lymphoid cells.

CD117 (c‑KIT) negativity is not inherently good or bad—its importance depends on the clinical context. In some tumors (for example GIST), CD117 positivity identifies a targetable receptor and guides therapy, so negativity can limit treatment options. In other settings, absence of CD117 may suggest a different diagnosis or prognosis. Discuss results and next steps with your treating clinician.