How Rare is Chronic Myelomonocytic Leukemia (CMML)?
CMML is a rare hematologic malignancy with an estimated annual incidence of approximately 1-2 cases per 100,000 adults, though it is likely underrecognized and underdiagnosed. 1
Epidemiologic Context
While specific incidence data for CMML is limited in the provided guidelines, the disease represents a small subset of myeloid malignancies:
CMML is classified as a rare myelodysplastic/myeloproliferative neoplasm (MDS/MPN) overlap syndrome by the WHO classification system 2, 1
The disease is likely underrecognized, meaning actual incidence may be higher than reported 1
CMML predominantly affects older adults, with a median age at diagnosis of approximately 73 years, making it primarily a disease of the elderly 3
Comparative Rarity
To contextualize CMML's rarity, consider that:
Chronic myeloid leukemia (CML), a different entity, has an incidence of 1.5-1.8 per 100,000 per year in the United States 2
CML accounts for approximately 15% of newly diagnosed adult leukemias 4
CMML represents an even smaller proportion of hematologic malignancies than CML, though exact comparative percentages are not specified in the guidelines 5
Clinical Implications of Rarity
The rarity of CMML creates several clinical challenges:
Diagnostic expertise is limited due to the small number of cases seen by most practitioners 5
Clinical trials have historically been difficult to conduct, with CMML patients often relegated to subpopulations within MDS studies rather than dedicated CMML trials 1
Recent years have seen increased dedicated research efforts specifically for CMML, reflecting growing recognition of this rare disease 1
Recent Diagnostic Changes
Updated 2022 diagnostic criteria lowered the monocyte threshold to 0.5 × 10⁹/L (from 1.0 × 10⁹/L), which will reclassify many cases previously diagnosed as MDS into CMML, potentially increasing recognized incidence 1