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Isolated trisomy 8 (+8) is a frequent cytogenetic abnormality in the myelodysplastic syndromes (MDS), but its characteristics are poorly reported. We performed a retrospective study of 138 MDS patients with isolated +8, classified or reclassified as MDS (excluding MDS/myeloproliferative neoplasm). Myeloproliferative (MP) features were defined by the repeated presence of one of the following: white blood cell count >10 × 109 /l, myelemia (presence of circulating immature granulocytes with a predominance of more mature forms) >2%, palpable splenomegaly. Fifty-four patients (39·1%) had MP features: 28 at diagnosis, 26 were acquired during evolution. MP forms had more EZH2 (33·3% vs. 12·0% in non-MP, P = 0·047), ASXL1 (66·7% vs. 42·3%, P = 0·048) and STAG2 mutations (77·8% vs. 21·7%, P = 0·006). Median event-free survival (EFS) and overall survival (OS) were 25 and 27 months for patients with MP features at diagnosis, versus 28 (P = 0·15) and 39 months (P = 0·085) for those without MP features, respectively. Among the 57 patients who received hypomethylating agent (HMA), OS was lower in MP cases (13 months vs. 23 months in non-MP cases, P = 0.02). In conclusion, MP features are frequent in MDS with isolated +8. MP forms had more EZH2, ASXL1 and STAG2 mutations, responded poorly to HMA, and tended to have poorer survival than non-MP forms.

JMML and CMML are rare myelodysplastic/myeloproliferative neoplasms occurring at both ends of life. To investigate relationships between JMML and CMML, genes recently involved in CMML were studied in 68 JMML patients. Mutations in TET2, RUNX1 and JAK2(V617F) are involved in myelodysplastic and/or myeloproliferative syndromes, and more specifically in CMML but were not found in JMML. Pangenomic analysis by SNP-array showed no abnormality at these loci. Three frameshift mutations of ASXL1 leading to a truncated protein were found in three patients (4%) with late onset JMML displaying also RAS activating mutations. Homozygous mutations of CBL with 11q loss of heterozygosity were found in five (7%) JMML. CBL substitutions were different from those reported in CMML, exclusive from other RAS activating mutations, and were germline in all patients. Overall, the pattern of genetic lesions observed in JMML differed from that of CMML. Although signalling deregulation is involved in CMML, transcriptional deregulation seems to play a pivotal role, with mutation of RUNX1, ASXL1 or TET2. Conversely, none of these genes involved in transcription or chromatin remodelling was found to be significantly altered in JMML, while CBL mutations confirm the central role of RAS and growth factor signalling deregulation in JMML.