Ruxolitinib treatment and risk of B‐cell lymphomas in myeloproliferative neoplasms

To the Editor: Myeloproliferative neoplasms (MPN), including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are clonal disorders complicated mainly by vascular events and transformation to myelofibrosis or leukemia.1 Secondary malignancies, in particular lymphoproliferative disorders, are rare but occur at a higher frequency than found in the general population.2-4 A previous study has shown that JAK1/2 inhibitor treatment in myelofibrosis is associated with an increased risk for aggressive B-cell lymphomas, and that detection of a preexisting B-cell clone might identify at risk individuals.5 Different findings were recently reported by the group of Pemmaraju: they performed a large database review of 2583 patients with MPN and did not find significant difference in the incidence of lymphoma when comparing patients who received JAK inhibitor therapy vs those who did not. Authors suggested that the discrepancy might depend on the larger size of the dataset, the longer duration of follow-up, the different treatment received for MPN (none of their patients received pipobroman), and demographic factors (American vs European cohorts).6 In an attempt to investigate in our cohort of patients with MPN the risk of developing lymphoproliferative disorders and the potential association with ruxolitinib therapy, we performed two strategies. First, we interrogated our MPN database to identify patients who developed lymphoproliferative disorders during follow-up. Within a cohort of 3069 consecutive patients with MPN (1027 PV, 1347 ET, 140 prePMF, 405 PMF, 114 secondary MF, 36 MPN not otherwise specified) followed for a median time of 6.7 years (0-41), we identified 24 patients who developed lymphoproliferative disorders during follow-up. None of the patients who developed lymphoma had prior therapy with ruxolitinib (P > .9), thus confirming the observation of Pemmaraju et al. Lymphoproliferative disorders were mostly of B-cell type (including four chronic lymphocytic leukemia), and only two T-cell lymphomas were observed. Twelve out of these 24 patients were previously exposed to alkylating agents (pipobroman or busulphan) for the treatment of the myeloid malignancy. None of the 85 patients treated with ruxolitinib (16 PV, 13 ET, 56 myelofibrosis) developed lymphoproliferative disorders during follow-up (median follow-up 12.5 years, range 0-30.6). The incidence of lymphoproliferative disorders in our cohort was compared with that of general population using the standardized incidence ratio (SIR), defined as the ratio between observed and expected cases. The expected number of lymphoproliferative disorders cases was estimated using sex and age incidence rates reported by the Global Cancer Observatory for Italy in 2018, applied to the corresponding person-years at risk. The incidence of lymphoproliferative disorders was significantly higher in our cohort than in general population (SIR: 3.69; 95% CI: 2.48-5.51; P < .001). This result was confirmed both in males (SIR: 4.49; 95% CI: 2.79-7.22; P < .001) and in females (SIR: 2.49; 95% CI: 1.19-5.22; P = .012). We next screened for B-cell clonality 38 MPN patients treated with ruxolitinib (11 ET, 13 PV, 14 myelofibrosis) for whom a biological sample before and after exposure to ruxolitinib was available. The analysis of immunoglobulin heavy chain gene variable (IGHV) rearrangements was performed using RNA extracted from peripheral blood mononuclear cells. The detection of a clonal IGHV rearrangement was assessed using the IGH Somatic Hypermutation Assay v2.0 kit (Invivoscribe, San Diego, California) and GeneScan analysis according to manufacturer's instructions. All patients were polyclonal before starting ruxolitinib; a clonal immunoglobulin rearrangement was detected only in 1 of 38 patients after treatment. This particular patient was affected with JAK2- and TET2-mutated postET myelofibrosis and had a familial history of MPN (father affected with ET). Because of resistance to hydroxyurea, in October 2009 she was enrolled in a clinical trial with ruxolitinib; treatment was discontinued in February 2012 due to progressive splenomegaly. The IGHV rearrangement (Figure 1) performed 7 months after discontinuation (2012) demonstrated the occurrence of B-cell clonality, confirmed in a subsequent sample 2 years later (2014). A sample collected in between (2013) was discordant, may be due to the sensibility of the assay (5%): the Invivoscribe assay cannot reliably detect less than 5 positive cells per 100 normal cells. In bone marrow biopsies, either before or after therapy, a minimal interstitial lymphoid component was observed (5% of the whole cellularity) and composed by T CD3+ lymphocytes with scattered small B CD20+, CD79a+ cells, interpreted as of reactive significance, not sufficient to hypothesize a diagnosis of lymphoid malignancy. A whole body computed tomography showed an asymptomatic paravertebral mass (D6-D10), interpreted as extramedullary hematopoiesis, due to its stability during follow-up (unchanged since the first description in 2010). This patient died in September 2014 due to MF in accelerated phase. In conclusion, the rate of lymphoproliferative disorders among MPN patients was low (24/3069 0.78%) but higher than expected in the general population and was not associated with a previous exposure to ruxolitinib. As none of our patients showed B-cell clonality on peripheral blood before ruxolitinib treatment, our findings reinforce the view that in the absence of B cell clones, ruxolitinib treatment may be considered relatively safe and can be initiated with close monitoring. The use of ruxolitinib in case of preexisting B-cell clonality needs further prospective studies. This work was supported by a grant from Italian Ministry of Health for young researchers (GR-2016-02361272) to E.R. and Associazione Italiana per la Ricerca sul Cancro AIRC 5x1000 project #21267 (MYNERVA project, http://www.progettoagimm.it) to M.C. Consulting and research funding from Novartis (E.R.), consulting from Celgene, Sandoz, advisory role from Celgene, Janssen-Cilag, Verastem and research funding from Gilead (L.A.). E.R. designed the research and wrote the paper. S.Z., R.R., C.F., D.P., and C.C. performed molecular investigations. E.B. performed histological evaluations. C.C., I.C.C., M.C., and C.T. collected clinical data; V.F. performed statistical analysis. M.C. and L.A. finalized the manuscript.