The different prognostic impact of type‐1 or type‐1 like and type‐2 or type‐2 like <i>CALR</i> mutations in patients with primary myelofibrosis
Authors: Bing Li, Zefeng Xu, Yan Li, Robert Peter Gale, Zhen Song, Xiaofei Ai, Tiejun Qin, Yue Zhang, Peihong Zhang, Gang Huang, Zhijian Xiao
Journal: American Journal of Hematology (2016)

To the Editor: Primary myelofibrosis (PMF) is a Philadelphia-chromosome-negative myeloproliferative neoplasm (MPN) in which JAK2V617F, CALR, and MPLW515 mutations are the most frequent driver mutations. CALR mutations were associated with younger age, more severe anemia, higher WBC and platelet levels, lower Dynamic International Prognostic Scoring System (DIPSS)-plus scores, and longer survival compared to subjects with JAK2 mutations 1. These CALR mutations involve exon 9 and were somatic insertions or deletions (indels). Type-1 (L367fs*46) and Type-2 (K285fs*47) CALR mutations were the most frequent. Some recent researches suggested potential differences among both types of mutations in mouse model 2. In clinical study, Tefferi et al. 3 showed that the favorable prognostic impact of CALR mutations may operate only in persons with Type-1 or Type-1 like mutations and that Type-2 or Type-2 like mutations had comparable survival compared to JAK2 mutations. The difference between the two types of CALR mutation remained significant after adjusting for age, ASXL1 or EZH2 mutations. However, Rumi et al. 4 observed no difference between Type-1 and Type-2 CALR mutations. Therefore, the prognostic impact of the two different types of CALR mutations is conflicting. In the current study, we focus on the prognostic impact of Type-1 or Type-1 like and Type-2 or Type-2 like mutations based on the data from a single center in China. The study was approved by the Ethical Committee of the Institute of Hematology, CAMS according to the guidelines of the Declaration of Helsinki. Four hundred and two subjects with PMF had a bone marrow sample collected at diagnosis or referral, February 1990 to February 2015 at the Institute of Hematology and Blood Disease Hospital, Chinese Academy of Medical Sciences were enrolled. Histological material was re-reviewed by a blinded pathologist and diagnosis was based on World Health Organization (WHO) criteria. Last follow up was date of last contact, date of death, or October 15, 2015. The DIPSS scores were calculated. JAK2, MPL, and CALR mutations were tested as reported. Follow-up data were available for 361 subjects. Median follow-up of survivors was 36 months (range, 1–385) months. Correlations between sample groups and clinical and laboratory data were calculated with the χ2 test for qualitative variables with discrete categories and the Mann–Whitney U-test or Kruskal–Wallis analysis of variance for continuous variables. Survival distributions were estimated by the Kaplan–Meier method and were compared between subgroups using the log-rank test. The Cox proportional hazards regression model was used to assess the correlation between variables and survival. JAK2V617F mutations were detected in 189 subjects (47%), MPLW515 mutations in 13 (3.2%), and CALR mutations in 81 (20.1%). One hundred and nineteen subjects (29.6%) had no detectable mutation in JAK2, MPL, or CALR. There were 30 (37%) Type-1, 48 (59.3%) Type-2, and 3 (3.7%) Type-1 like CALR mutations. Subjects with Type-1 or Type-1 like and Type-2 CALR mutations were compared to those with JAK2 mutations (Supporting Information Table I). Subjects with CALR Type-1 or Type-1 like mutations were younger (P = 0.06), had lower hemoglobin concentrations (P = 0.012), lower WBC levels (P < 0.001). Subjects with CALR Type-2 mutations were younger (P = 0.009), had lower hemoglobin concentrations (P = 0.001), lower WBC levels (P < 0.001), less splenomegaly (P = 0.002), and higher DIPSS (P = 0.013). Ten-years prospective survival was 64% in JAK2-mutant, 93% in Type-1 or Type-1 like CALR-mutant, and 53% in Type-2 CALR-mutant patients, as shown in Fig. 1. Overall survival (OS) was significantly briefer in subjects with Type 2 (P = 0.004, HR 6.9, 95% CI 1.9–25.4) when compared with subjects with Type 1 or Type-1 like CALR mutations (Fig. 1). Compared with subjects with JAK2 mutations, OS was longer in patients with Type 1 or Type-1 like (P = 0.082, HR 0.3, 95% CI 0.1–1.2), and was briefer in those with Type-2 (P = 0.007, HR 2.3, 95% CI 1.3–4.1) CALR mutations (Fig. 1). Kaplan–Meier analysis of overall survival of PMF patients stratified according to JAK2 and CALR mutations. In mutivariate survival analyses, subjects with CALR Type-2 mutation (P = 0.046, HR 1.8, 95% CI 1.01–3.37) had significantly briefer survival compared with subjects with JAK2 mutations after adjusting for DIPSS. And those with CALR Type-1 or Type-1 like mutation were likely to have longer survival compared with subjects with JAK2 mutations (P = 0.062, HR 0.29, 95% CI 0.076–1.065). In summary, our findings support previous report in Teferri et al. study that the prognostic advantage of CALR mutation in PMF regards only patients harboring Type-1 or Type-1 like mutations, although the difference was of borderline significance for Type-1 or Type-1 like CALR mutant vs. JAK2-mutant. A relatively small number of CALR Type 1/Type 1-like mutated subjects in our study might hamper a significant difference for survival. Moreover, we found that subjects with Type-2 mutations had briefer survival compared to JAK2V617F-mutated subjects and the difference remained significant after adjusting for DIPSS. Recently, Guglielmelli et al. 5 also reported the prognostic advantage of Type-1 or Type-1 like CALR mutant and similar survival between Type-2 or Type-2 like CALR mutant and JAK2V617F-mutant in 251 patients from one Italian center. The difference in prognostic impact of Type-2 mutation between our findings and previous reports should be further validated. Tefferi et al. 6 found the significant association of EZH2 and IDH mutations with Type-2 CALR mutations. Therefore, the prognostic impact of subclonal mutations should be taken into account in PMF patients. We are using next generation sequencing in our subjects with CALR mutations to explore the different prognostic impact between Type-1 or Type-1 like and Type-2 or Type-2 like CALR mutations. Bing Li,1,2 Zefeng Xu,1,2 Yan Li,1 Robert Peter Gale,3 Zhen Song,4 Xiaofei Ai,5 Tiejun Qin,1 Yue Zhang,1,2 Peihong Zhang,6 Gang Huang,7 and Zhijian Xiao1,2* 1MDS and MPN Centre, Institute of Hematology and Blood Diseases Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Tianjin, China; 2State Key Laboratory of Experimental Hematology, Institute of Hematology and Blood Diseases Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Tianjin, China; 3Division of Experimental Medicine, Department of Medicine, Imperial College London, Haematology Research Center, London, United Kingdom; 4Medical Service Division, Institute of Hematology and Blood Diseases Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Tianjin, China; 5Molecular Diagnostic Laboratory, Institute of Hematology and Blood Diseases Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Tianjin, China; 6Department of Pathology, Institute of Hematology and Blood Diseases Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Tianjin, China; 7Division of Experimental Hematology and Cancer Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio Additional Supporting Information may be found in the online version of this article. Supporting Information Table 1. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.