Composite chronic myeloid leukemia and essential thrombocythemia with BCR-ABL1 fusion and CALR mutation

Chronic myeloproliferative neoplasms with concomitant CALR mutation and BCR::ABL1 translocation: diagnostic and therapeutic implications of a rare hybrid disease

Myeloproliferative neoplasms (MPNs) are subdivided into Philadelphia (Ph) chromosome-positive chronic myeloid leukemia (CML) and Ph-negative MPNs. BCR::ABL1 translocation is essential for the development and diagnosis of CML; on the other hand, the majority of Ph-negative MPNs are characterized by generally mutually exclusive mutations of Janus kinase 2 (JAK2), calreticulin (CALR), or thrombopoietin receptor/myeloproliferative leukemia (MPL). CALR mutations have been described essentially in JAK2 and MPL wild-type essential thrombocythemia and primary myelofibrosis. Rarely coexisting CALR and MPL mutations have been found in Ph-negative MPNs. BCR::ABL1 translocation and JAK2 mutations were initially considered mutually exclusive genomic events, but a discrete number of cases with the combination of these genetic alterations have been reported. The presence of BCR::ABL1 translocation with a coexisting CALR mutation is even more uncommon. Herein, starting from a routinely diagnosed case of CALR-mutated primary myelofibrosis subsequently acquiring BCR::ABL1 translocation, we performed a comprehensive review of the literature, discussing the clinicopathologic and molecular features, as well as the outcome and treatment of cases with BCR::ABL1 and CALR co-occurrence.

Hereditary thrombocythemia due to splicing donor site mutation of THPO in a Japanese family

Thrombopoietin (THPO) is an essential factor for platelet production. Hereditary thrombocythemia (HT) is caused by a germline mutation of THPO, MPL, or JAK2 and is inherited in an autosomal-dominant manner. We identified a Japanese family with HT due to a point mutation of the splicing donor site of the THPO gene (THPO c.13 + 1G > A). Bone marrow biopsy showed increased megakaryocytes mimicking essential thrombocythemia. One affected family member developed chronic myeloid leukemia. We cloned the mutation and developed mutated and wild type THPO expression vectors. Molecular analysis showed that the mutation causes an exon 3 skipping transcript of THPO that abrogates a suppressive untranslated upstream open reading frame. Although the transcript levels of THPO mRNA were comparable, mutated transcripts were more efficiently translated and THPO protein expression was significantly higher than that of the wild type.

Insights from a rare myeloproliferative neoplasm with coexisting BCR-ABL1 fusion gene, CALR, and TET2 mutations treated with nilotinib and ruxolitinib

Myeloproliferative neoplasms (MPNs) with concurrent BCR-ABL1 fusion gene and CALR mutation are especially rare. We report a patient with coexisting BCR-ABL1 fusion gene, CALR, and TET2 mutations who was treated with the combination of the second-generation TKI nilotinib and JAK1/JAK2 inhibitor ruxolitinib.

Philadelphia+ Chronic Myeloid Leukemia with CALR Mutation: A Case Report and Literature Review

Myeloproliferative neoplasms (MPNs) are classified as chronic myeloid leukemia (CML) and Philadelphia chromosome-negative MPN. In MPN cases, the presence of a BCR-ABL1 translocation with a coexisting mutation is exceptionally rare. Herein, we report the first documented patient with CML harboring CALR mutation in Korea. A 33-year-old woman was referred to our hospital in February 2015 with splenomegaly, leukocytosis, and thrombocytosis. She was diagnosed with CML and started receiving nilotinib. In October 2015, a major molecular response was observed, but thrombocytosis persisted. A repeat bone marrow (BM) examination revealed no specific findings. However, as thrombocytosis worsened, we changed nilotinib to dasatinib. In May 2019, owing to persistent thrombocytosis, we repeated the BM examination and found CALR mutation (15.97%) on the MPN–next generation sequencing (NGS) test. We then retrospectively performed repeat MPN-NGS testing using the BM aspirate sample obtained in 2015 and found CALR mutation (10.64%).

Atypical myeloproliferative neoplasm with concurrent BCR-ABL1 fusion and CALR mutation: A case report and literature review

RATIONALE

Concurrent calreticulin (CALR) mutation and BCR-ABL1 fusion are extremely rare in chronic myelogenous leukemia; to date, only 12 cases have been reported.

PATIENT CONCERNS

A 57-year-old male who had an 11-year history of essential thrombocytosis presented to our hospital with leukocytosis and marked splenomegaly for 3 months.

DIAGNOSES

Chronic myelogenous leukemia with myeloid fibrosis arising on the background of essential thrombocytosis harboring both BCR-ABL1 fusion and type-1 like CALR mutation.

INTERVENTIONS

Imatinib was started at 300 mg daily and increased to 400 mg daily after 3 months; interferon was added after 12 months.

OUTCOMES

Partial cytogenetic response was achieved after 3 months of imatinib therapy and complete cytogenetic response was achieved after 1 year of treatment. However, CALR mutation was still present with a stable mutational allele burden.

LESSONS

In this case report and review of additional 12 cases with simultaneous presence of CALR-mutation and BCR-ABL1 fusion, we highlighted the importance of integrating clinical, morphological, and molecular genetic data for classifying atypical myeloid neoplasms.