The 2016 WHO versus 2008 WHO criteria for the diagnosis of chronic myelomonocytic leukemia

The 2016 WHO diagnostic criteria for chronic myelomonocytic leukemia (CMML) require both absolute and relative monocytosis (≥1×10⁹/L and ≥10% of white blood cell counts) in peripheral blood. Moreover, myeloproliferative neoplasm (MPN) features in bone marrow and/or MPN-associated mutations tend to support MPN with monocytosis rather than CMML. We assessed the impact of the 2016 WHO criteria on CMML diagnosis, compared with the 2008 WHO criteria, through a retrospective review of the medical records of 38 CMML patients diagnosed according to the 2008 WHO classification. Application of the 2016 WHO criteria resulted in the exclusion of three (8%) patients who did not fulfill the relative monocytosis criterion and eight (21%) patients with an MPN-associated mutation. These 11 patients formed the 2016 WHO others group; the remaining 27 formed the 2016 WHO CMML group. The significant difference in the platelet count and monocyte percentage between the two groups indicated that the 2016 WHO criteria lead to a more homogenous and improved definition of CMML compared with the 2008 WHO criteria, which may have led to over-diagnosis of CMML. More widespread use of molecular tests and more sophisticated clinical and morphological evaluations are necessary to diagnose CMML accurately.