HRAS and acute myeloid leukemia: HRAS mutations are thus rarely found in myeloid malignancies, whereas mutations leading to oncogenic KRAS or NRAS activation occur in ~ 40% of cases with chronic myelomonocytic leukemia [5] and in 20% of cases of monocytic (FAB classes M4 and M5) forms of acute myeloid leukemia (AML) [5–7].