Oligomonocytic chronic myelomonocytic leukemia (OM-CMML) is defined as those myelodysplastic syndromes (MDSs) or myelodysplastic/myeloproliferative neoplasms, unclassifiable with relative monocytosis (≥10% monocytes) and a monocyte count of 0.5 to <1 × 109/L. These patients show clinical and genomic features similar to those of overt chronic myelomonocytic leukemia (CMML), although most of them are currently categorized as MDS, according to the World Health Organization 2017 classification. We analyzed the clinicopathologic features of 40 patients with OM-CMML with well-annotated immunophenotypic and molecular data and compared them to those of 56 patients with overt CMML. We found similar clinical, morphological, and cytogenetic features. In addition, OM-CMML mirrored the well-known complex molecular profile of CMML, except for the presence of a lower percentage of RAS pathway mutations. In this regard, of the different genes assessed, only CBL was found to be mutated at a significantly lower frequency. Likewise, the OM-CMML immunophenotypic profile, assessed by the presence of >94% classical monocytes (MO1s) and CD56 and/or CD2 positivity in peripheral blood monocytes, was similar to overt CMML. The MO1 percentage >94% method showed high accuracy for predicting CMML diagnosis (sensitivity, 90.7%; specificity, 92.2%), even when considering OM-CMML as a subtype of CMML (sensitivity, 84.9%; specificity, 92.1%) in our series of 233 patients (39 OM-CMML, 54 CMML, 23 MDS, and 15 myeloproliferative neoplasms with monocytosis and 102 reactive monocytosis). These results support the consideration of OM-CMML as a distinctive subtype of CMML.

Genetic studies in patients with Philadelphia-negative myeloproliferative neoplasms (MPNs) are essential to establish the correct diagnosis and to optimise their management. Recently, it has been demonstrated that it is possible to detect molecular alterations analysing cell-free DNA (cfDNA) in plasma samples, which is known as liquid biopsy. We have assessed the molecular profile of a cohort of 107 MPN patients [33 polycythaemia vera (PV), 56 essential thrombocythaemia (ET), 14 primary myelofibrosis (PMF) and 4 unclassifiable MPN] by next-generation sequencing (NGS) using cfDNA and paired granulocyte DNA. A high concentration of cfDNA in plasma was observed in patients with high molecular complexity, in MPL-mutated cases, and in PMF patients. Targeted sequencing of cfDNA showed a comparable mutational profile (100% accuracy) to the one obtained in granulocytic DNA and a strong correlation was observed between the variant allele frequency (VAF) of gene mutations in both DNA sources. The median VAF detected in cfDNA (29Á0%; range: 0Á95-91Á73%) was significantly higher than the VAF detected in granulocytes (median 25Á2%; range: 0Á10-95Á5%), especially for MPL mutations (44Á3% vs. 22Á5%). In conclusion, our data support the use of cfDNA as a fast, sensitive and accurate strategy for performing molecular characterisation of MPN patients.

Oligomonocytic chronic myelomonocytic leukemia (OM-CMML) patients are currently classified into the different categories of the 2017 WHO MDS classification. However recent data support considering OM-CMML as a specific subtype of chronic myelomonocytic leukemia (CMML) given their similar clinical, genomic and immunophenotypic profiles. The main purpose of our study was to provide survival outcome data of a well-annotated series of 42 patients with OM-CMML and to compare them to 162 patients with CMML, 120 with dysplastic type (D-CMML) and 42 with proliferative type (P-CMML). OM-CMML showed significantly longer overall survival (OS) and acute myeloid leukemia-free survival than CMML patients considered as a whole group, and when compared to D-CMML and P-CMML, respectively. Moreover, gene mutations associated with increased proliferation (i.e.: ASXL1 and RAS-pathway mutations) were identified as independent adverse prognostic factors for OS in our series. We found that at a median follow-up of 53.47 months, 29.3% of our OM-CMML patients progressed to D-CMML, and at a median follow-up of 46.03 months, 28.6% of our D-CMML progressed to P-CMML. These data support the existence of an evolutionary continuum among OM-CMML, D-CMML and P-CMML. In this context, we observed that harboring more than 3 mutated genes, ASXL1 mutations and a peripheral blood monocyte percentage above 20% significantly predicted shorter time of progression of OM-CMML into overt CMML. These variables were also detected as independent adverse prognostic factors for OS in OM-CMML. These data support the consideration of OM-CMML as the first evolutionary stage within the proliferative continuum of CMML.

Fig 2. VAF in granulocytes (GR), saliva and CD3+ lymphocytes for JAK2, CALR and MPL mutated cases.

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Molecular and cytogenetic studies are essential in patients with myelodysplastic syndromes (MDS) for diagnosis and prognosis. Cell-free DNA (cfDNA) analysis has been reported as a reliable non-invasive approach for detecting molecular abnormalities in MDS, however, there is limited information about cytogenetic alterations and monitoring in cfDNA. We have assessed the molecular and cytogenetic profile of a cohort of 70 patients with MDS by next-generation sequencing (NGS) using cfDNA and compared the results to paired bone marrow (BM) DNA. Sequencing of BM DNA and cfDNA showed a comparable mutational profile (92.1% concordance) and variant allele frequencies (VAF) strongly correlated between both sample types. Of note, SF3B1 mutations were detected with significantly higher VAF in cfDNA than in BM DNA. NGS and microarrays were highly concordant to detect chromosomal alterations although with lower sensitivity than karyotype/FISH. Nevertheless, all cytogenetic aberrations detected by NGS in BM DNA were also detected in cfDNA. Additionally, molecular and cytogenetic alterations were monitored and we observed an excellent correlation between the VAF of mutations in BM DNA and cfDNA across multiple matched time points. A decrease in the cfDNA VAF was detected in patients responding to therapy, but not in non-responding patients. Of note, cfDNA analysis also showed cytogenetic evolution in 2 cases not responding to treatment. In conclusion, although further studies with larger cohorts are required, our results support the analysis of cfDNA as a promising strategy for performing molecular characterization, detection of chromosomal aberrations and monitoring of MDS patients.

INTRODUCTION The 2017 WHO classification requires the presence of ≥1x109/L and ≥10% of monocytes in peripheral blood (PB) for the diagnosis of CMML. Recently, Geyer et al. defines oligomonocytic CMML (O-CMML) as those MDS cases with relative monocytosis (≥10% monocytes) and monocyte count 0.5<1x109/L. The authors showed that clinicopathologic and mutational profile of OCMML were similar to overt CMML. The study of PB monocyte subsets by flow cytometry (FC) has gained interest for CMML diagnosis. As showed by Selimoglu-Buet et al, the increase of classical monocytes (Mo1) >94% is a highly sensitive and specific diagnostic marker for CMML. In the extent of our knowledge, there are no data about PB monocyte subset distribution by FC in O-CMML. Moreover, CD2 and CD56 expression is common in CMML and rarely observed in MDS, the group where O-CMML are currently included. Furthermore, we compared: the molecular profile; cytogenetic abnormalities; cytopenias; BM dysplasia; BM blast and monocyte percentage; PB monocyte percentage, and monocyte and leukocyte counts. METHODS 50 CMML and 33 O-CMML from a single institution were prospectively studied from 02/2016 to date. Table 1 summarizes morphologic, cytogenetic, molecular and clinical findings. We studied PB monocyte subsets by FC: Mo1 (CD14bright/CD16-), Mo2 (CD14bright/CD16+) and Mo3 (CD14dim or -/CD16bright). In addition, we assessed the expression of CD56 and CD2 in monocytes (positivity ≥ 20%). Finally, targeted NGS of the entire exonic sequence of 25 genes recurrently mutated in myeloid malignancies was performed (VAF sensitivity: 2%). Chi-Square, Fisher exact or Man-Whitney U tests were used as appropriate. RESULTS AND DISCUSSION The Mo1 percentage (%) was significantly inferior in O-CMML (P=0.007), but it is noteworthy that median and mean of Mo1% in O-CMML were upper the cutoff of 94% (median: 96.1 vs 98.1; mean: 94.7 vs 96.9). Moreover, the % of patients with >94% Mo1 was no significantly different when comparing O-CMML and CMML although a clear trend was observed (72% vs 90%; P=0.082). This result is impressive since, as previously reported, the specificity of the Mo1 >94% test is around 90-95% and only 5-10% of false positive rate (FP) should be expected. However, in O-CMML a 72% of FP was observed since following 2017 WHO recommendation these patients should be considered as MDS. No differences were observed neither in the % of patients showing CD56+ monocytes (65.6% vs 66.7%; P=0.923) nor in the % of them showing CD2+ (28.1% vs 37.5%; P=0.53) when comparing O-CMML and CMML. We observed no significant differences in platelet count, hemoglobin, BM dyserythropoiesis, BM dysgranulopoiesis, BM dysmegacaryopoiesis, BM blast %, percentage of abnormal karyotypes, and Spanish cytogenetic risk stratification. The main differences were observed in leukocyte count, monocyte count, PB monocyte %, BM monocyte %, and BM promonocyte percentage. Table 1. There were no differences in the number of mutated genes or in the number of mutations between CMML and O-CMML (Table 1). As expected, TET2 and SRSF2 were the most frequently mutated genes in both groups. Moreover, no significant difference was observed in the presence of TET2/SRSF2 co-mutation, the gene signature of CMML (32% vs 26% in CMML). The genes mutated at a frequency >10% in O-CMML were: TET2 (79%), SRSF2 (36%), SF3B1 (29%), ZRSR2 (25%), DNMT3A (15%), and ASXL1 (14%). The genes mutated at a frequency >10% in CMML were: TET2 (81%), SRSF2 (28%), ASXL1 (23%), CBL (23%), SF3B1 (16%), and NRAS (14%). Only two genes were mutated at a significant different frequency: CBL (4% vs 23% in CMML, P=0.041) and ZRSR2 (25% vs 7% in CMML, P=0.043). As expected, CMML showed a higher % of RAS pathway mutations (CBL, NRAS or KRAS) since these have been associated with proliferative features (4% vs 40%, P=0.001). This is especially evident in proliferative CMML in which genes associated with proliferation are present at higher frequencies: CBL (4% vs 39% in CMML, P=0.01), NRAS (0 vs 23% in CMML, P=0.029) and ASXL1 (14% vs 62% in CMML, P=0.004). A significant lower percentage of O-CMML with ZRSR2mut presented Mo1 >94% (33% vs 86%, P=0.024). As shown, O-CMML without ZRSR2mut showed this feature in a similar percentage than CMML (86% vs 90%). At a median follow-up of 31.2 months, 19% of O-CMML evolved to CMML showing a median time to evolution of 34 months. CONCLUSION Our data support the diagnosis of O-CMML as a distinctive subtype of CMML. Table 1 Disclosures Bellosillo: Qiagen: Consultancy, Speakers Bureau; TermoFisher Scientific: Consultancy, Speakers Bureau.

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