The main purpose of this project is to study the uptake pattern of FLT-PET in cases, and it is value in assessing the malignant hematopoiesis in cases of Pre-PMF and ET, regarding diagnosis, staging and monitoring response to therapy. Identifying different patterns of uptake in patients with Pre-PMF and ET in various clinical settings.

Evaluating FLT-PET as a novel non-invasive technique in cases with Pre-PMF and ET, in comparison to the standard bone marrow biopsy about disease diagnosis, assessment of disease activity, detection of transformation, monitoring of treatment response and grading of fibrosis.Study the ability of FLT-PET to differentiate between Pre-PMF and ET.

the investigators also aim to examine the association of FLT-PET uptake patterns with different genetic makeup (JAK2 (Janus kinase 2), CALR (Calreticulin), MPL (myeloproliferative leukemia protein), or Triple negative disease) or allele burden in cases of Pre-PMF and ET.

PET with fluorodeoxy glucose combined with computed tomography is a major tool for the diagnosis, staging, and monitoring of treatment response in clinical oncology. 3'-18Fluoro-3'-deoxy-L-thymidine (18F-FLT) is a PET radiotracer that quickly accumulates in proliferating cells and can be used to assess tumor cell proliferation in various cancers as PET radiotracer offers a non-invasive assessment of cell proliferation in vivo.

Myeloproliferative Neoplasms (MPNs) are clonal hematopoietic stem disorders characterized by high rate of effective proliferation of one or more cell lineage. MPNs are overlapping syndromes that can progress to fibrotic stage or evolute into acute leukemia. Preliminary results of a pilot study (5) suggested that this technique could be useful to assess bone marrow (BM) activity and extramedullary hematopoiesis in patients with Myelofibrosis (MF).

The current standard for follow- up of these patients is based on pathological markers (peripheral blood counts and/ bone marrow histomorphology) and molecular markers. Although, bone marrow examination could be considered as a standard gold method as it gives detailed information about cellularity, the morphology of each lineage, a degree of fibrosis, transformation and dysplastic features. However, many patients are reluctant to go for this invasive technique which precludes precise assessment of disease activity at the desirable frequencies. Non- invasive techniques which may act as the good clinical surrogate are lacking.

The objective of this study is to study the uptake pattern of FLT-PET in cases, and it is value in assessing the malignant hematopoiesis in cases of Pre-PMF and ET, regarding diagnosis, staging and monitoring response to therapy.

Identifying different patterns of uptake in patients with Pre-PMF and ET in various clinical settings.

Evaluating FLT-PET as a novel non-invasive technique in cases with Pre-PMF and ET, in comparison to the standard bone marrow biopsy about disease diagnosis, assessment of disease activity, detection of transformation, monitoring of treatment response and grading of fibrosis.

Study the ability of FLT-PET to differentiate between Pre-PMF and ET. the investigators also aim to investigate the association of FLT-PET uptake patterns with different genetic makeup (JAK2, CALR, MPL, or Triple negative disease) or allele burden in cases of Pre-PMF and ET.

Inclusion Criteria:

Age 18 year old or above Patient accept to sign inform consent ECOG (Eastern Cooperative Oncology Group) performance less than or equal 2

• Cases fulfilling WHO (World Health Organization) 2016 diagnostic criteria for PMF:

WHO criteria for prefibrotic/early primary myelofibrosis (prePMF)

Major criteria:

1. Megakaryocytic proliferation and atypia, without reticulin fibrosis > grade 1*, accompanied by increased age-adjusted BM cellularity, granulocytic proliferation and often decreased erythropoiesis
2. Not meeting the WHO criteria for BCR-ABL1+ ((BCR-ABL = fusion gene from BCR (breakpoint cluster region gene/BCR gene product) and ABL (Abelson proto-oncogene)) CML (chronic myelogenous leukemia), PV (Polycythemia Vera), ET, myelodysplastic syndromes, or other myeloid neoplasms
3. Presence of JAK2, CALR or MPL mutation or in the absence of these mutations, presence of another clonal marker**or absence of minor reactive BM reticulin fibrosis.

Minor criteria:

Presence of at least one of the following, confirmed in two consecutive determinations:

1. Anemia not attributed to a comorbid condition
2. Leukocytosis >11 x 109/L
3. Palpable splenomegaly
4. LDH (Lactate dehydrogenase) increased to above upper normal limit of institutional reference range.

Diagnosis of prePMF requires meeting all three major criteria, and at least one minor criterion **in the absence of any of the 3 major clonal mutations, the search for the most frequent accompanying gene mutations (e.g. ASXL1, EZH2, TET2, IDH1/IDH2, SRSF2, SF3B1) are of help in determining the clonal nature of the disease.

*** minor (grade 1) reticulin fibrosis secondary to infection, autoimmune disorder or other chronic inflammatory conditions, hairy cell leukemia or other lymphoid neoplasm, metastatic malignancy, or toxic (chronic) myelopathies

WHO diagnostic criteria essential thrombocythemia Major criteria Platelet count ≥450 × 109/L Bone marrow biopsy showing proliferation mainly of the megakaryocyte lineage with increased numbers of enlarged, mature megakaryocytes with hyperlobulated nuclei. No significant increase or left shift in neutrophil granulopoiesis or erythropoiesis and very rarely minor (grade 1) increase in reticulin fibers.

Not meeting WHO criteria for BCR-ABL1+ CML, PV, PMF, myelodysplastic syndromes, or other myeloid neoplasms Presence of JAK2, CALR, or MPL mutation Minor criterion Presence of a clonal marker or absence of evidence for reactive thrombocytosis Diagnosis of ET requires meeting all 4 major criteria or the first 3 major criteria and the minor criterion

Exclusion Criteria:

• Patient not fulfilling the inclusion criteria.
• Vulnerable groups: pregnant, minors, prisoners will not be included.
• Bone marrow will be collected as part of the routine diagnostic work-up. No extra bone marrow material will be collected solely for the aim of the study.