CALR mutation

Thrombotic and hemorrhagic complications represent the most common cause of morbidity in MPNs, however the mechanisms underlying this pathology remain opaque. Cytoreduction and antithrombotic therapies, the mainstay for treatment of MPNs, inadequately address platelet dysfunction, though emerging therapies targeting the MPN clone are promising. Thus, a deeper understanding of megakaryocyte and platelet biology in MPNs is essential for the development of precise therapeutic strategies to reduce thrombotic complications and improve patient outcomes.

Recent therapeutic advances increasingly aim to move beyond pathway-level cytoreduction toward disease modification and clonal control, including interferon-based strategies, mutation-selective approaches targeting oncogenic JAK2 or mutant CALR, and allele-directed therapeutic concepts currently under clinical and preclinical development. This review synthesizes recent advances in the genetic architecture, clonal evolution, and therapeutic targeting of Ph-negative MPNs, with particular emphasis on integrating mutational profiling and functional biomarkers to refine diagnosis, guide disease-modifying therapies, and enable mechanism-aligned molecular monitoring.

Overall, clinical information gained from calreticulin testing is greatest when it is used in an integrated clinicopathologic and molecular testing context rather than as a standalone test. To make calreticulin mutations more effectively used for diagnosis or prognosis in routine hematology practice, we need standardization of testing, harmonization of reporting, and prospective validation of risk-models based on both the subtypes and the burden of the mutation.

HRM-CALR-AI combines open-set recognition with low-cost HRM to detect rare and unreported variants at ~50-fold lower cost and same-day turnaround. Multicenter reproducibility and benchmarking against fragment analysis support implementation as a frontline screening tool where NGS access is limited.

Importantly, dose reduction of both palbociclib and pegIFNα maintained efficacy in MPN samples while minimizing cytotoxicity in control hematopoietic cells, revealing a favorable therapeutic window. These findings highlight the potential of combining CDK6 inhibition with pegIFNα to enhance anti-neoplastic effects in MPNs and support a novel potential approach to improve MPN therapy.

This case highlights the limitations of routine assays focused on common CALR mutations and supports comprehensive sequencing-based approaches for detecting rare CALR variants. Expanded molecular testing may improve diagnostic accuracy and clinical classification in MPNs.

Emerging combination strategies and their clinical development will be reviewed here, including investigations that pair JAKi therapy with BCL-2 family inhibitors, BET inhibitors, restored p53 cell death signals, telomerase inhibitors, PIM1 kinase inhibitors, and mutant CALR targeted therapies. While several combination clinical trials suggest improved spleen and symptom responses and the possibility of disease modification, toxicity profiles and optimal sequencing remain areas of active investigation.

The CALR mutation was lower among females, and was associated with lower leukocyte counts, and Hb and Hct levels, and with higher platelet counts. In multivariable analysis, the apparent protective association of CALR with thrombosis was not independent.

Preclinical and early clinical advances - including monoclonal antibodies, bispecific T-cell engagers, CAR-T therapies, antibody-drug conjugates, and peptide/viral vector vaccines - have demonstrated selective activity against CALR-mutant clones while sparing normal hematopoiesis, with encouraging evidence of molecular remissions and disease modification. Although challenges such as immune tolerance remain, mutant CALR-directed therapies represent a potential transformative shift in essential thrombocythemia, and primary myelofibrosis treatment.

In multivariable analysis, TP53 mutations and higher peripheral blast burden adversely affected OS, while CALR mutations appeared to be associated with improved OS, peripheral blasts also independently predicted relapse. These data underscore the cure rate of approximately one-third of MPN-BP and highlight peripheral blasts and TP53 as actionable risk markers for transplant strategies.

In contrast, gDNA is more informative in confirming treatment response. The lymphocyte percentage predicts cfDNA utility, enabling rational test selection and a practical framework for optimizing MPN management.