Table 1.

Diagnostic criteria for JMML per 2016 WHO classification (guideline used when this case presented).

I: Clinical and hematologic features (all 4 features mandatory)	II: Genetic studies (1 finding sufficient)	III: For patients without genetic features, besides the clinical and hematologic features listed under I, the following criteria must be fulfilled
PB monocyte count ≥1 × 109/L	Somatic mutation in PTPN11∗ or KRAS∗ or NRAS∗	Monosomy 7 or any other chromosomal abnormality or at least 2 of the following criteria:
Blast percentage in PB and BM <20%	Clinical diagnosis of neurofibromatosis type 1 or NF1 mutation	Haemoglobin F increased for age
Splenomegaly	Germ line CBL mutation and loss of heterozygosity of CBL†	Myeloid or erythroid precursors on PB smear
Absence of Philadelphia chromosome (BCR::ABL1 rearrangement)		GM-CSF hypersensitivity in colony assay
		Hyperphosphorylation of STAT5

^∗Germline line mutations (indicating Noonan syndrome) need to be excluded. ^†Occasional cases with heterozygous splice site mutations. Note. updates were published in the 5^th edition of the World Health Organization Classification of Haematolymphoid Tumors. The changes to the diagnostic criteria of JMML include (i) absence of KMT2A rearrangements as one of the required diagnostic criteria; (ii) elimination of monosomy 7 as a cytogenetic criterion; (iii) hypersensitivity to GM-CSF by colony assay and STAT5 hyperphosphorylation combined as one minor criterion; (iv) thrombocytopenia with hypercellular bone marrow added as one minor criterion [2].