Yoon HS, et al. J Korean Med Sci. 2020 Sep;35(39):e350. https://doi.org/10.3346/jkms.2020.35.e350

Somatic CALR mutations occur in approximately 70% of patients with JAK2 V617F-negative essential thrombocythemia (ET) and primary myelofibrosis (PMF). We evaluated the effects of the CALR mutant type and burden on the phenotype of CALR-mutated myeloproliferative neoplasms (MPN). Of the 510 patients with suspected or diagnosed MPN, all 49 patients detected with CALR mutations were diagnosed with ET (n = 32) or PMF (n = 17). The CALR mutant burden was significantly higher in PMF than in ET (45% vs. 34%), and type 1-like and type 2-like mutations were detected in 49% and 51% patients, respectively. Patients with MPN and type 2-like mutation showed a significantly higher median platelet count than those with type 1-like mutation. Particularly, patients with ET and type 2-like mutation had no thrombotic events, despite higher platelet counts. The effect of CALR mutant burden differed depending on the mutant type. A higher mutant burden tended to be associated with a cytopenic phenotype (i.e., lower hemoglobin levels and platelet counts) in patients with the type 1-like mutation and a proliferative hematological phenotype (i.e., higher platelet and neutrophil counts) in patients with the type 2-like mutation. This study suggests that the disease phenotype of MPN may be altered through CALR mutant burden and mutant type.

Ha-eun Cho, M.D., Yujin Han, M.D., Ph.D., Jae Joon Lee, M.D., Ph.D., Kyung Sun Park, M.D., Ph.D., Young Jin Kim, M.D., Ph.D., Sun Young Cho, M.D., Ph.D., Hoi Soo Yoon, M.D., Ph.D., Woo-In Lee, M.D., Ph.D., and Tae Sung Park, M.D., Ph.D.. Ann Lab Med 2022;42:485-7. https://doi.org/10.3343/alm.2022.42.4.485