Chronic Myelomonocytic Leukemia With Preexisting Myelodysplastic Syndrome Or Myeloproliferative Neoplasm: Two Stages Of One Disease With Poor Prognosis

Introduction Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic malignancy characterized by persistent monocytosis with features of a myelodysplastic syndrome (MDS) and/or myeloproliferative neoplasm (MPN). While most cases present as de novo disease, a subset of CMML has been described in the literature to evolve from a preexisting MDS (MDS-CMML). CMML with preexisting MPN (MPN-CMML) has not been characterized to our knowledge. It is uncertain whether CMML patients with preexisting MDS or MPN have one or more disease processes and if such patients behave differently from patients who present with de novo CMML. In an attempt to address these questions, we compared the clinicopathologic features between groups of MDS-CMML, MPN-CMML, and de novo CMML in the present study. Methods 126 cases with newly diagnosed CMML were retrieved from our database over a 3-year period. 22 cases had preexisting MDS (n=15) or MPN (n=7). Prior diagnoses of MDS included refractory anemia (n=5), refractory anemia with ring sideroblasts (n=2), MDS with isolated 5q deletion (n=1), refractory cytopenia with multilineage dysplasia (n=6), and refractory anemia with excess blasts-1 (n=1). Prior diagnoses of MPN included essential thrombocythemia (n=1), primary myelofibrosis (n=3), and MPN NOS (n=3). Cytogenetic studies were performed in all cases. Other parameters obtained included age, gender, hemoglobin, white blood cell count, monocytes, platelets, bone marrow blasts and histology, and JAK2/MPL mutations. 22 consecutive cases of de novo CMML were included for comparative analysis. Results CMML with preexisting MDS or MPN comprised 17% of CMML (22/126 patients). Among these 22 patients, 15 were male and 7 female with a median age of 79 (range 61-86) years. Median age of the patients at CMML stage was similar to that of patients with de novo CMML (77 years; range 65-89). The median time between disease presentation as MDS or MPN and CMML was 22 months. Patients presented with marked monocytosis at the CMML stage (mean: 23% and 4564/uL) as compared to the stage of MDS (mean: 13% and 794/uL; p<0.001) or MPN (mean: 6.4% and 1216/uL; p<0.001); and the monocyte count was similar to that present in de novo CMML (mean: 24% and 4313/uL). Marrow blasts were significantly increased at the CMML stage as compared to the stage of MDS (mean: 5.3 vs. 1.6; p=0.017), MPN (mean: 5.1 vs. 1.9; p=0.048), or de novo CMML (5.2 vs. 1.9; p=0.009). There was no significant difference in average hemoglobin, platelet count or marrow cellularity between cases at the two disease stages or among the MDS-CMML and MPN-CMML subgroups. However, the marrows of MPN-CMML showed significantly increased diffuse reticulin fibrosis (p=0.002) and marked megakaryocytic hyperplasia (p=0.002) as compared to MDS-CMML. CMML with preexisting MDS or MPN is more frequently associated with cytogenetic abnormalities than de novo CMML (50% vs. 23%), although this difference did not reach statistical significance (p=0.116). 8 (36%) cases had chromosome abnormalities at the MDS or MPN stages; 7 (87%) of the 8 cases demonstrated persistent chromosome abnormalities at the CMML stage. In addition, 4 (18%) patients acquired chromosome abnormalities at the CMML stage. JAK2 mutation was seen in 1 (7%) of 15 cases of MDS-CMML and 4 (57%) of 7 cases of MPN-CMML. Notably, 2 cases of JAK2 positive MPN became JAK2 negative at the CMML stage; one of the patients had been previously treated with a JAK2 inhibitor. No MPL mutation was found in any case. Conclusions CMML with preexisting MDS or MPN is not uncommon. The majority of cases exhibit persistent chromosomal abnormalities from the preexisting MDS or MPN, supporting the notion of one disease with two stages of presentation. The findings of a higher frequency of cytogenetic abnormalities and occasional cytogenetic evolution may suggest that chromosome alteration is one of the mechanisms involved in triggering disease progression to CMML. JAK2 V617F was more frequent in MPN-CMML, which correlated with myelofibrosis and megakaryocytic hyperplasia. However, loss of JAK2 mutation can occur at CMML stage. Loss/inhibition of JAK2 activity may contribute to a change in disease course. Our study revealed that CMML with preexisting MDS or MPN is characterized by more advanced disease with increased marrow blasts and therefore may be associated with a poorer prognosis. Disclosures: No relevant conflicts of interest to declare.