Clinical Charactistics of Ph-Negative MPN Patients with Coexistence of JAK2V617F, Calr and MPL Mutation
Authors: Ma Dan , Liu Ping , Pan Chengyun , Cheng Bingqing , Zhang Yaming , Wang Yan , Hu Xiuying , Wang Jishi 
Published: November 2020

Background and purpose: JAK2, CALR and MPL gene mutations are the driver genes leading to the pathogenesis of ph-negative myeloproliferative meoplasm (MPN). However, it's still unkonwn about the effect of double gene mutations coexisting in ph-negative MPN patients. In this study, we analyzed the clinical significance of the three driver gene mutations when they coexisted in patients with MPN.
Methods: Collected bone marrow or peripheral blood samples of 221 patients with suspected MPN who were in the Affiliated Hospital of Guizhou Medical University between May 2017 and April 2020; qPCR detection for JAK2V617F mutation and sanger sequencing detection for CALR gene exon 9 and MPL Exon 10 mutation. Searched Pubmed database related to the coexistence of the three driver gene mutations and extracted information; Fisher exact test to analyze the differences in clinical characteristics between double mutation carriers and single mutation carriers. Shapiro-Wilk statistical analysis of the differences in clinical characteristics of ET patients with different types of double mutations.
Results: 1 ET and 1 PMF patient carried both JAK2V617F and CALR gene mutations were found in our center, accounting for 0.9% of ph-negative MPN. The CALR carried by PMF patients was a newly discovered mutation type, c.1126_1127insTTTGC, R376Lfs*56. Through database search, we collected 26 literatures involving MPN case reports with double-driver gene mutations. By fitting analysis with the clinical information of positive patients in our center, a total of 74 MPN patients were collected, of which the number of ET patients was the largest(57/74, accounting for 77.03%). The most common coexisting mutant type was JAK2V617F plus CALR (63/74, 85.14%). The age of onset of MPN patients with double-driver gene mutations was significantly higher than that of single-mutation carriers, and the proportion of patients over 70 years of age was higher (p&lt;0.05), and double mutation carriers had higher platelet count levels(Plt) (p&lt;0.05). The proportion of patients with splenomegalia was lower (p&lt;0.05). The clinical characteristics of ET patients were similar to MPN patients, but no difference in the incidence of splenomegalia (p&gt;0.05). Among PMF patients, the Plt and the proportion of patients with megasplenomegaly in double mutation carriers were similar to those in MPN patients, but the hemoglobin(Hb) was higher (p&lt;0.05). In addition, we also compared the clinical characteristics of ET patients with different gene mutation types. The results showed that the Hb of patients with JAK2V617F and CALR mutations were higher than those of ET patients with JAK2V617F and MPL mutations (p&lt;0.05), but the Plt level is low (p&lt;0.05). Although there were no significant differences in age, gender, IPSET-thrombosis and IPSET (IWG-MRT) scores and WBC between the two groups, the proportion of female ET patients with JAKV617F with MPL mutation was significantly higher than that of JAK2V617F with CALR mutation group (p&lt;0.05). And the proportion of patients with WBC exceeding 11×109/L was also higher (p&lt;0.05). In addition, only one PV patient carried JAK2V617F and CALR, and achieved partial or complete remission after treatment with standard treatment regimens (hydroxyurea or interferon-α).
Conclusion: JAK2V617F, CALR and MPL gene mutations are not mutually exclusive in MPN patients, but a certain number of double mutation carriers are ignored. Compared with patients with single-gene mutations, patients with double-gene mutations are older and have higher platelet counts, and should be treated differently in later treatment. At the same time, there are also differences between ET patients with different mutation combinations. These results suggest that it is very necessary for MPN patients to check for three driver gene mutations at the same time, and this type of patients may become a new subtype of MPN.

Disclosures
No relevant conflicts of interest to declare.