Concurrent or Sequential BCR-ABL Translocation and Calr gene or JAK2V617F Mutation
Authors: Pagoni Maria , Garofalaki Maria , Tziotziou Irene , Nikolou Evaggelia , Karakatsanis Stamatis , Tsonis Ioannis , Zoi Katerina , Baltathakis Ioannis , Karakasis Dimitrios , Harhalakis Nikolaos 
Published: October 2019

Abstract
The detection of concurrent JAK2V617F and BCR-ABL mutations is uncommon; an incidence of 2.5% is reported in the literature. Scarce data indicate that the coexistence of JAK2V617F mutation and BCR-ABL translocation may denote an adverse prognostic factor for CML. Recently, the occurrence of novel Calreticulin (CALR) mutations in JAK2/MPL unmutated ET or PMF was reported. To our knowledge, no CALR mutations have been described so far in the context of BCR-ABL positive MPNs. We present 3 cases with molecularly defined diagnosis of another type of MPN in addition to Ph+ CML, including one patient with the novel finding of a CALR mutation in conjunction with the BCR-ABLtranslocation, and we infer a possible mechanism for the emergence of a second MPN clone upon treatment of the initial MPN.
A 32 yr old female was diagnosed in 1999 with ET on the basis of marked thrombocytosis in the absence of any underlying cause. She was treated with INF-α and subsequently with anagrelide. Six years later (2005) and while the CBC was normal, cytogenetic and molecular studies disclosed the presence of Ph1 chromosome in 4/20 metaphases and BCR-ABL transcripts (7.2% IS, e15a2). Imatinib was initiated and after 3 months CCyR and MMR were achieved. Due to an increasing platelet count one year later, a trephine biopsy was performed that was compatible with ET. Hydroxyurea (HU) was added to treatment. No JAK2V617F mutation was detected. Fifteen years after the initial presentation, a CALR exon 9 mutation was retrospectively detected in all available samples since diagnosis of CML. The mutant allele burden has remained stable during follow-up, while patient being in MR4 with regard to CML.
A 50 yr old woman was diagnosed with PV in 1998. Cytogenetic studies were normal and BCR-ABL was undetectable. JAK2V617F homozygous mutation was present on retrospective testing. A complete hematologic remission was achieved with phlebotomy and HU. Ten years later, re-evaluation due to an increasing WBC disclosed the presence of Ph1 chromosome in 20/20 metaphases and BCR-ABL transcripts (38.4% IS, e15a2). Interestingly, JAK2V617F was not detected. After 4 months of treatment with TKI plus HU, a 2-log BCR-ABL reduction was noted, while JAK2V617F was detected again at a heterozygous state. She received sequentially all 3 first available TKIs due to intolerance. Upon TKI treatment for 9 months, CCyR and MMR were achieved in parallel with emergence of JAK2V617F homozygosity. After achieving MR4 for more than 2 years, the TKI was discontinued and, 3 months later, the patient remains in MR4 with persistent JAK2V617F homozygosity. Due to splenomegaly and increased Hct, treatment with HU is continuously required.
An 80 yr old female was diagnosed with chronic phase CML [Ph1+, BCR-ABL (35.5% IS, e15a2)]. She achieved mCyR and 1-log reduction of BCR-ABL levels after 6 months on imatinib. Due to imatinib failure, she was switched to nilotinib at 9 months. Two years after initial diagnosis, while CML was in MMR, an increase in Hct and platelets was noticed and JAK2V617F heterozygosity was detected. Retrospective analysis did not reveal JAK2V617F mutation at diagnosis and on the 3-month sample, while low level of mutant V617F allele was detected on the 6-month sample. Increasing levels of mutant versus wild type allele were detected in all subsequent samples. The patient was treated with phlebotomy, HU and ASA in addition to nilotinib. She died 4 years after initial diagnosis from an unrelated cause while in MR4 for CML and complete hematologic remission for PV.
Despite these cases seem to be uncommon, they raise intriguing issues regarding the clonal origins of distinct molecular types of MPNs present in the same patient. They may also challenge the traditional hypothesis of evolution of one type of MPN to another. Instead of perceiving clinical and genetic features of second MPN as simple evolution of a precedent MPN, our cases suggest an alternative explanation based on pre-existence of two different MPN clones. Treatment for the initial MPN, especially with highly-efficient targeted agents (like TKIs for Ph+ CML) may facilitate the emergence of a second clone and vice versa. In conclusion, any divergent manifestations in a patient with MPN may warrant further investigation of genetic markers suggestive of an additional MPN entity. A high level of suspicion for the possibility of coexistence Ph+ and Ph- MPN may result in a more comprehensive treatment approach and optimal outcome.

Disclosures
No relevant conflicts of interest to declare.