Researchers have demonstrated the importance of conducting CD117 and CD25 immunohistochemical staining after chemotherapy induction to screen systemic mastocytosis with associated hematological neoplasm (SM-ANH), particularly in patients with the KIT variant, as published in Annals of Laboratory Medicine.

In systemic mastocytosis, the proliferation of mast cells accumulates in the organs. SM-ANH is difficult to diagnose because other nonmast cell lineage hematological malignancies are usually present, which can mask systemic mastocytosis. These include myelodysplastic syndrome, acute myeloid leukemia, and myeloproliferative neoplasm. 

Immunohistochemical staining plays an important role in diagnosing systemic mastocytosis via the identification of mast cell aggregates. These aggregates can be identified with CD117 staining and aberrant CD25. The authors of the study decided to further investigate these claims.

They recruited 23 patients who were diagnosed with acute myeloid leukemia, 4 of whom were also diagnosed with SM-ANH. KIT variants were present in 6 patients with acute myeloid leukemia.

Read more about SM etiology 

To evaluate whether SM-ANH and acute myeloid leukemia diagnoses were concurrent, the research team conducted immunohistochemical staining for CD117 and CD25 on bone marrow samples. This was made possible because all patients diagnosed with SM-ANH had follow-up bone marrow tests.

At the time of acute myeloid leukemia diagnosis, patients with SM-AHN did not demonstrate evident mast cell aggregation on hematoxylin-eosin slides. However, immunohistochemical staining on bone marrow samples revealed the presence of mast cell aggregates with CD117 expression and aberrant CD25 expression in the patients in whom the studies were conducted.

Concomitant SM-AHN was diagnosed in 17.4% of patients with acute myeloid leukemia with RUNX1::RUNX1T1 via CD117 and CD25 immunohistochemistry staining in postinduction bone marrow sections. The research team discovered that the clinical characteristics and the overall survival of acute myeloid leukemia patients with and without SM-ANH did not differ significantly, although KIT variants were more commonly observed in patients with SM-ANH. 

“It is necessary to screen mast cell aggregates for CD117 expression and subsequently for CD25 expression through [immunohistochemistry] staining of samples collected from [acute myeloid leukemia] patients with RUNX1::RUNX1T1 after induction,” Hwang and colleagues concluded.


Hwang SM, Kim BJ, Lee JS, et al. Immunohistochemical staining to identify concomitant systemic mastocytosis in acute myeloid leukemia with RUNX1::RUNX1T1Ann Lab Med. 2022;42(6):678-682. doi:10.3343/alm.2022.42.6.678