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JAK2 V617F mutation to calreticulin mutation in an essential thrombocythemia patient: A case report
Su-Yun Wang1, Ning Yang2, Li-Jun Zhang3, Zhi-Yong Cheng3
1 Department of Hematology, Shenzhen Longhua District Central Hospital, Shenzhen, Guangdong Province, China
2 Department of General Surgery, The No.1 Hospital of Baoding, Baoding, Hebei Province, China
3 Department of Hematology, The No.1 Hospital of Baoding, Baoding, Hebei Province, China
|Date of Submission||08-Feb-2020|
|Date of Decision||13-Feb-2020|
|Date of Acceptance||04-Sep-2020|
|Date of Web Publication||16-Jul-2021|
Department of Hematology, The No.1 Hospital of Baoding, Baoding, Hebei Province
Source of Support: None, Conflict of Interest: None
Essential thrombocythemia (ET) is a type of myeloproliferative neoplasm (MPN) that is negative for the BCR-ABL1 fusion gene. It is characterized by clonal expansion of hematopoietic precursor cells followed by increased production of megakaryocytes and platelets in the bone marrow. Patients with ET often have spontaneous skin and mucous membrane bleeding, along with thrombosis and spleen enlargement. In some patients, ET can progress into leukemia.
Recent studies further identified that most ET patients without Janus kinase 2 (JAK2) or myeloproliferative leukemia (MPL) mutations have calreticulin (CALR) gene mutation in exon 9.
In general, the JAK2, MPL, and CALR mutations are mutually exclusive, with multiple mutations in the same MPN patient occurring infrequently. In rare cases, associations of such mutations are found within one MPN patient. Here, we describe the genetic evaluation of an ET patient with the occurrence of multiple mutations. Briefly, the patient was determined initially to be positive for JAK2 V617F. After treatment, the JAK2 clone mutation disappeared, and a CALR mutation was identified. To the best of our knowledge, this is the first case of mutual mutations in two genes occurring in a patient with ET.
| » Case|| |
A 63-year-old man presented to our hospital in May 2009 with episodic dizziness along with a 2-month history of increased weakness and fatigue. He had been diagnosed with diabetes mellitus and hypertension 20 years prior and had a cerebral infarction with no sequelae 2 years ago. Current pharmacotherapy comprised intermediate-acting insulin and oral nifedipine sustained-release. On examination, he was found to have splenomegaly below the subcostal margin. Full blood count revealed a hemoglobin concentration of 148 g/L (reference range: 130 – 175 g/L), white blood cells 4.0 – 10.0×109/L (reference range: 4.0 – 10.0×109/L), and platelet count of 1205 × 109/L (reference range: 100-350×109/L). A blood film and bone marrow smear showed thrombocytosis [Figure 1], while a bone marrow aspirate demonstrated megakaryocytic hyperplasia and morphological atypia without fibrosis and negative reticulin stain [Figure 2]. A heterozygous JAK2 V617F mutation was detected and the JAK2 V617F burden was 0.4. Mutations in the CALR (examined by bone marrow pathological biopsy in April 2009), MPL (W515K/L), and BCR-ABL1 fusion genes were not detected by gene sequencing or quantitative polymerase chain reaction (PCR). The chromosomal karyotype was normal (46XY). The patient was diagnosed with ET and treated with hydroxyurea intermittently and interferon-α for 4–6 months annually from May 2009 to March 2014 and achieved complete hematological remission. In March 2014, the patient terminated interferon therapy. In March 2015, he represented following increased weakness and fatigue with thrombocytosis over the preceding month. Key parameters from his full blood count were hemoglobin 130 g/L, white cell count 5.23 ×109/L, and platelet count 565 × 109/L. A bone marrow aspirate showed increasing megakaryocytes with hyperlobulated nuclei without fibrosis. A heterozygous mutation within CALR-EX0N9 p.K385fsX47 was detected but without JAK2 V617F or MPL W515K/L mutations, or variations in the BCR-ABL1 fusion gene. Treatment continued with hydroxyurea, and interferon-α alfa was recommenced. In 5 years, this patient remained in complete hematologic remission, and the CALR mutation was still present.
|Figure 1: Bone marrow smear. Bone marrow smear showed increased numbers of megakaryocytes and thrombocytosis without any other abnormalities|
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|Figure 2: Bone marrow biopsy. Bone marrow biopsy showed megakaryocytic hyperplasia and morphological atypia without fibrosis|
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ET is a BCR-ABL1-negative MPN that mainly involves megakaryocyte lineage and is manifested by an increase in platelet count in peripheral blood. This proliferation is thought to occur in association with JAK2 V617F, MPL W515 K/L, and CALR gene mutations in up to 70–90% of ET cases. The presence of CALR gene variants in patients with MPN who lack JAK2 and MPL gene mutations has provided an additional diagnostic and prognostic tool for this disease. In MPN, CALR mutations consist of an exon-9 somatic insertion or deletion resulting in the formation of two common variants: L367fs*46 or K385fs*47. The CALR mutation is stem cell-derived, mostly heterozygous, and generally mutually exclusive of JAK2 and MPL mutations except for rare cases. The two common variants of the CALR mutation accounted for 53% and 32% of all mutations, respectively. Here, we describe a patient with ET who carried the JAK2 V617F mutation and transformed to CALR exon-9 mutations during the course of time of his disease. Due to thrombocytosis associated with thrombosis, the patient was diagnosed with JAK2 V617F-positive ET in 2009. At this point in time, the CALR mutation had not been discovered. Interferon has an antitumor effect and good curative effects in MPN patients with JAK2 V617F or CALR mutations. In clinical trials, approximately 80% of MPN patients had a hematologic response to interferon-α, along with a reduction in JAK2 V617F and CALR mutant expression levels and potential risk of transformation to leukemia. Some patients even achieved molecular remission. In our case, the JAK2 V617F mutation was associated with a response to interferon-α, and molecular remission was attained. The patient's platelet count remained steady with no new thrombosis, and he became JAK2 V617F mutation-negative following 5 years of interferon-α treatment. Interferon-α selectively targets the malignant clone in a subset of MPN patients and can induce both hematological and molecular remission in ET patients with the JAK2 V617F mutation.
In the sixth year of our patient's disease, progression occurred with increased platelets and thrombosis recurrence. He remained negative for the JAK2 V617F mutation but had the emergence of the CALR mutation. At this time, we reviewed the patient's baseline bone marrow specimen done from 6 years prior and determined that he was originally negative for the CALR mutation. So, we considered that treatment with interferon-α was associated with the JAK2 mutation becoming negative, with the emergence of new mutations in CALR due to interruption of treatment. After recommencing interferon-α, the patient's platelets remained stable within the normal range and without disease progression until now.
Previous studies have shown that the JAK2 V617F mutation is associated with tyrosine kinase activity and can spontaneously activate the downstream signaling pathway, JAK2-STAT5. The CALR mutation can enhance interleukin-3 expression in vitro to promote STAT5 phosphorylation, which can be blocked by JAK inhibitors. Further, interferon-α is effective in treating MPN patients with CALR mutations. Therefore, it has been suggested that CALR and JAK2 mutations may have similar mechanisms. However, CALR, JAK2, and MPL mutations are mutually exclusive, and it is very rare to have co-expression. Now new JAK inhibitors, such as ruxolitinib, have been used alone or in combination with interferon-α to treat MPNs. It can be used not only in JAK2 mutation patients but also in other types of MPN patients with MPL or CALR mutations.
Declaration of patient consent
Written informed consent was obtained from the patient for publication of this manuscript and any accompanying images.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]