Pregnancy Management and Outcomes in Patients with Myeloproliferative Neoplasms

Introduction: While BCR-ABL1 negative myeloproliferative neoplasms (MPN) are typically diagnosed in the sixth decade of life, approximately 20% of patients are diagnosed before the age of 40 years. Patients with MPN of reproductive age are being increasingly encountered in clinical practice. Concurrently, there has been increased awareness of the risks of pregnancy complications in patients with MPN and the importance of MPN-specific management to help mitigate these risks. MPN are associated with thrombotic and hemorrhagic complications, and pregnancy may amplify the thrombotic risk. Additionally, MPN may be associated with an increased risk of placental dysfunction and associated complications of preeclampsia, fetal growth restriction, preterm delivery and fetal loss. The aim of this observational study was to report on pregnancy outcomes in a modern cohort of patients with MPN managed according to consensus recommendations. Methods: We conducted a retrospective review of patients with MPN and pregnancy evaluated at either the Princess Margaret Cancer Centre or Mount Sinai Hospital in Toronto, Canada between January 1, 2010 and December 31, 2020. Diagnoses were defined according to the WHO 2016 criteria using information available from hospital records. Descriptive statistics were used to describe selected baseline characteristics. Categorical variables were summarized with counts and percentages. Results: A total of 32 patients with MPN and pregnancy were included in the study (Table 1). The median age at the time of the index pregnancy was 33 (range 21 - 45) years. The most common MPN diagnosis was essential thrombocythemia (ET, n=15), followed by polycythemia vera (PV, n=9) and primary myelofibrosis (PMF, n=8). Driver mutation data was available for 30 patients: 17 (57%) had mutated JAK2, 5 (17%) CALR, and 9 (30%) had no driver mutation identified. Five patients had a prior history of venous thrombosis, all of which were portal vein thrombosis, and 2 patients had a history of bleeding events. Information on antenatal treatment was available for 22 patients: 18 (82%) patients received aspirin, 3 (14%) received antenatal low molecular weight heparin (LMWH) and 3 (14%) received interferon (IFN; interferon alpha 2b in 2 cases and pegylated interferon alfa 2a in 1); 16 (73%) received post-partum LMWH. Information on maternal complications was available for 22 patients. There were 2 thrombotic events (1 antepartum and 1 postpartum) and 1 postpartum hemorrhage. There were no cases of preeclampsia. Of 22 pregnancies, there were 19 live births (86%), 2 first trimester losses (9%) and 1 second trimester loss (5%). Gestational age was 37 weeks or more in 16/17 (94%) and was 33 weeks for 1 patient. Vaginal deliveries were performed in 11/20 (55%) cases and 9/20 (45%) were Cesarean deliveries. Discussion: This observational study represents a modern cohort of MPN patients treated according to consensus recommendations. Our findings highlight that MPN patients have better pregnancy outcomes than those previously described in the literature. Limitations of this retrospective study include a small sample, missing data, and potential underreporting of early pregnancy loss. Pregnancy in patients with MPN is associated with unique risks that may be reduced with interventions such as antepartum aspirin, IFN in higher risk patients, and postpartum LMWH. That not all standard risk patients were managed with aspirin and postpartum LMWH suggests educational opportunities exist for hematologists and maternal-fetal medicine physicians involved in the care of these patients. Figure 1 Figure 1. Disclosures Gupta: Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS-Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Honoraria; Pfizer: Consultancy; Roche: Consultancy; Constellation Pharma: Consultancy, Honoraria; Sierra Oncology: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Research Funding. Malinowski: Alexion: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy. Maze: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene-BMS: Honoraria; Takeda: Research Funding; PharmaEssentia: Research Funding; Kronos Bio: Research Funding.

Myeloproliferative Neoplasms (MPN) Clonal Evolution Landscape and Its Impact on Patients' Prognosis

Introduction: Although myeloproliferative neoplasms (MPN) are driven by three mutually exclusive driver mutations (JAK2, CALR and MPL), targeted deep sequencing studies identified multiple additional somatic mutations potentially impacting MPN evolution. Presence of a high molecular risk (HMR: ASXL1, EZH2, SRSF2 and IDH1/2) or a TP53 mutations has been associated with adverse prognosis. However, to date, the effect of clonal evolution (CEv) on MPN patients' outcome has not been evaluated, as most of the studies assessed mutational-based prognosis stratification from single baseline molecular genotyping. The objective of our study was to describe the clinical and molecular characteristics of patients with CEv in a large cohort of MPN patients and analyze its impact on patients' outcome. Methods: A total of 1538 consecutive patients were diagnosed with MPN according to WHO criteria and followed in our hospital between January 2011 and January 2021. From this large retrospective cohort, we included in this study 446 patients who had at least 2 molecular analyses during the chronic phase of MPN, performed at diagnosis and/or during follow-up using next generation sequencing (NGS), targeting a panel of 36 genes involved in myeloid malignancies. Significant variants were retained with a sensitivity of 1%. CEv was defined as the acquisition of a new additional non-driver mutation between baseline and subsequent NGS evaluation. Statistical analyses were performed using the STATA software (STATA 17.0 for Mac Corporation, College Station, TX). Results: The median age at MPN diagnosis in our whole cohort was 51 years [IQR 41 - 60]. Our cohort included 167 (37%), 205 (46%) and 64 (14%) patients with polycythemia vera, essential thrombocythemia and primary myelofibrosis (MF) respectively. With a median interval of 1.6 years [IQR 1.0 - 2.8] between the first and the second NGS analysis in the whole cohort, CEv occurred in 128 patients (29%). Patients with CEv were significantly older compared to patients without CEv (n=318) (p=0.03). MPN diagnosis, the type of driver mutation and complete blood counts at MPN diagnosis did not differ between the 2 groups. Eighty-one (63%) and 198 (62%) patients with or without CEv respectively had at least one additional non-driver mutation at baseline NGS (p=0.59), while the rate of HMR (n=25 (20%) versus n=79 (25%)) or TP53 (n=7 (5%) versus n=20 (6%)) mutations at baseline NGS did not differ between the 2 groups. Thirty six out of 128 (28%) of patients with CEv had more than 1 acquired mutation. Most recurrently acquired mutations involved the epigenetic regulators TET2 and DNMT3A that were mutated in respectively 33% and 25% of patients with CEv (Figure 1A). Moreover, 38% of CEv patients acquired HMR (ASXL1 (14%), EZH2 (6%), SRSF2 (3%), IDH1/2 (2%)) or TP53 (13%) mutations. After a median follow up of 10.8 years [IQR 6.6 - 17.2] in the whole cohort representing a total of 5635 patient years, 32 (7%) patients died, and 11 (2.5%) and 11 (2.5%) patients with at least 2 NGS performed during MPN chronic phase transformed respectively into secondary MF or myelodysplastic syndrome / acute myeloid leukemia (MDS/AML). Interestingly, CEv (HR 11.27, 95%CI [5.09; 24.96], p<0.001) (Figure 1B), age at MPN diagnosis (HR 1.11, 95%CI [1.07; 1.15], p<0.001) and the presence of HMR mutations at baseline NGS (HR 4.48, 95%CI [2.05; 9.77], p <0.001) independently adversely impacted OS in a COX regression multivariate analysis. CEv also independently adversely impacted MDS/AML free survival (HR 13.15, 95%CI [3.88; 44.47], p<0.001) and secondary MF free survival (HR 21.13, 95%CI [6.18; 72.20], p<0.001) in a COX regression multivariate analysis. Conclusion: Our study on a large retrospective clinically and biologically annotated real-life cohort of MPN patients with long-term follow up shows that CEv independently adversely impacts OS, MDS/AML and secondary MF free survivals. CEv occurred in a clinically relevant proportion of MPN patients (28%) and was associated with patients' age. Acquired mutations mainly involved epigenetic regulators, HMR and TP53 genes. These results suggest that serial molecular monitoring using NGS could be routinely implemented in MPN patients follow up, to assess more accurately disease evolution and potentially update therapeutic management. Figure 1 Figure 1. Disclosures Raffoux: PFIZER: Consultancy; CELGENE/BMS: Consultancy; ABBVIE: Consultancy; ASTELLAS: Consultancy. Kiladjian: Novartis: Membership on an entity's Board of Directors or advisory committees; Taiho Oncology, Inc.: Research Funding; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Incyte Corporation: Membership on an entity's Board of Directors or advisory committees; PharmaEssentia: Other: Personal fees; AOP Orphan: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees. Benajiba: Gilead: Research Funding; Pfizer: Research Funding.

Clinical Features and Long-Term Outcomes in a Molecularly-Annotated Cohort of Adolescents and Young Adults with Myeloproliferative Neoplasms

Background: Myeloproliferative neoplasms (MPNs) are a heterogenous group of chronic hematologic malignancies that lead to morbidity and early mortality primarily due to thrombotic complications and progression to acute leukemia. Clinical and mutational risk factors have been demonstrated to predict outcomes in patients with MPNs, and are used commonly to guide therapeutic decisions (including allogenic stem cell transplant) in myelofibrosis. Adolescents and young adults (AYA, age ≤45 years) comprise less than 10% of all MPN patients, and have unique clinical and therapeutic considerations. The prevalence and clinical impact of somatic mutations implicated in myeloid disease has not been extensively reported in this population. Methods: We conducted a retrospective review of patients evaluated at the Princess Margaret Cancer Centre (PMCC) between 1/1/2000 and 30/6/2021 for an MPN diagnosed at ≤45 years of age. Diagnoses were defined per 2016 WHO criteria using available information on chart review. Targeted mutational profiling of clinically relevant myeloid genes (49- or 54-gene panel) was previously performed on peripheral blood or bone marrow samples. Pathologic variants in ASXL1, EZH2, IDH1/2, SRSF2, and U2AF1 Q157 were categorized as high-molecular risk (HMR). Categorical variables were compared using the χ2 test. Kaplan-Meier method was used for overall survival (OS) and time-to-event analysis; and were compared using the log-rank test. Results: A total of 237 patients with initial MPN diagnosis ≤45 years were included in the study, with median age of diagnosis 35 (range 12-45) years. MPN diagnosis included: essential thrombocythemia (ET, n=100), polycythemia vera (PV, n=75), prefibrotic primary myelofibrosis (Pre-PMF, N=29), overt PMF (n=24), and MPN-unclassifiable (MPN-u, n=9). Driver mutation data, available for 230 (97%) patients, were: JAK2 in 134 (56%), CALR in 70 (30%), MPL in 6 (2.5%), and triple-negative in 20 (8.4%) patients. Median follow-up was 10.2 (range 0.3-45.3) years, and median OS was the shortest for those with overt PMF (21.4 years, P=0.001) compared with PV (33.0 years), ET (31.4 years), and Pre-PMF (median OS not reached). No difference in OS based on driver mutation was observed. Progression to a secondary MF (SMF) was observed in 84 patients (47% of ET, 48% of PV) after median time of 19.7 years; with no difference in time to progression due to diagnosis or driver mutation. Progression to an accelerated/blast phase (AP/BP) was observed in 26 patients and was associated with diagnosis of overt PMF (P=0.04) and triple-negative for driver mutation (P=0.04). Thrombosis was observed in 61 (26%) patients: 34 (14%) patients with thrombosis prior to/concurrent with MPN diagnosis, and 34 (14%) patients with thrombosis after diagnosis. Splanchnic circulation thrombosis was found in 29 (12%) patients and 12 (5%) patients had Budd-Chiari syndrome. Portal hypertension was reported in 37 (16%) patients. CALR type-2 mutations were associated with the lowest frequency of total thrombosis (4%, P=0.02); while JAK2 had the greatest frequency of splanchnic circulation clot (17%, P=0.03). Targeted mutational profile was obtained for 202 (85%) of patients: 135 samples obtained during the initial disease phase, 51 samples during a secondary MF phase, and 16 during an AP/BP. For the patients with mutation analysis in the initial phase, 24 pathogenic mutations were observed in 16 (12%) patients including 3 patients with HMR mutations. The most frequent mutations observed were in TET2 (n=12, 9%), and ASXL1 (n=3, 2%). Presence of additional mutations did not predict OS, AP/BP progression, or thrombosis; though TET2 mutation was associated with shorter time to SMF progression in patients with PV/ET (P=0.002). Additional mutations were found in 34/51 (67%) patients in whom mutational analysis was first performed during a SMF disease phase. Conclusions: A long-term follow-up study of a large molecularly annotated cohort of AYA patients with MPN demonstrated excellent long-term survival for these patients. Overt PMF is associated with the lower OS and higher risk of AP/BP transformation. Thrombotic complications including splanchnic circulation thrombosis are frequent complications. Mutations aside from JAK2/MPL/CALR are uncommon and HMR mutations rare in the initial phase of MPN in the AYA population. Figure 1 Figure 1. Disclosures Gupta: Roche: Consultancy; Pfizer: Consultancy; AbbVie: Consultancy, Honoraria; BMS-Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sierra Oncology: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Research Funding; Constellation Pharma: Consultancy, Honoraria. Maze: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene-BMS: Honoraria; Takeda: Research Funding; PharmaEssentia: Research Funding; Kronos Bio: Research Funding.

A Recurrent STAT5BN642H Driver Mutation in Feline Alimentary T Cell Lymphoma

Alimentary lymphomas arising from T cells are rare and aggressive malignancies in humans. In comparison, they represent the most common anatomical form of lymphoma in cats. Due to the low prevalence in humans, the underlying pathomechanism for these diseases is poorly characterised, limiting experimental analysis and therapeutic exploration. To date, activating mutations of the JAK/STAT core cancer pathway and particularly the STAT5B oncoprotein have been identified in human enteropathy-associated T cell lymphoma. Here, we describe a high homology of human and feline STAT3 and STAT5B proteins and strong conservation at the genomic level. Analysis of 42 samples of feline T cell alimentary lymphoma reveals broad activation of STAT3 and STAT5B. Screening for known activating mutations in STAT3 or STAT5B identifies the presence of the STAT5BN642H driver mutation in feline enteropathy-associated T cell lymphoma in 7 out of 42 (16.67%) samples in total. Regarding lymphoma subtypes, the majority of mutations with 5 out of 17 (29.41%) cases were found in feline enteropathy-associated lymphoma type II (EATL II). This identification of an oncogenic STAT5B driver mutation in felines recapitulates the genetic situation in the corresponding human disease, thereby establishing the cat as a potential new model for a rare and incurable human T cell disease.

Extreme value theory as a framework for understanding mutation frequency distribution in cancer genomes

Currently, the population dynamics of preclonal cancer cells before clonal expansion of tumors has not been sufficiently addressed thus far. By focusing on preclonal cancer cell population as a Darwinian evolutionary system, we formulated and analyzed the observed mutation frequency among tumors (MFaT) as a proxy for the hypothesized sequence read frequency and beneficial fitness effect of a cancer driver mutation. Analogous to intestinal crypts, we assumed that sample donor patients are separate culture tanks where proliferating cells follow certain population dynamics described by extreme value theory (EVT). To validate this, we analyzed three large-scale cancer genome datasets, each harboring > 10000 tumor samples and in total involving > 177898 observed mutation sites. We clarified the necessary premises for the application of EVT in the strong selection and weak mutation (SSWM) regime in relation to cancer genome sequences at scale. We also confirmed that the stochastic distribution of MFaT is likely of the Fréchet type, which challenges the well-known Gumbel hypothesis of beneficial fitness effects. Based on statistical data analysis, we demonstrated the potential of EVT as a population genetics framework to understand and explain the stochastic behavior of driver-mutation frequency in cancer genomes as well as its applicability in real cancer genome sequence data.

Beyond the Driver Mutation: Immunotherapies in Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are a subtype of soft tissue sarcoma (STS), and have become a concept of oncogenic addiction and targeted therapies.The large majority of these tumors develop after a mutation in KIT or platelet derived growth factor receptor α (PDGFRα), resulting in uncontrolled proliferation. GISTs are highly sensitive to imatinib. GISTs are immune infiltrated tumors with a predominance of tumor-associated macrophages (TAMs) and T-cells, including many CD8+ T-cells, whose numbers are prognostic. The genomic expression profile is that of an inhibited Th1 response and the presence of tertiary lymphoid structures and B cell signatures, which are known as predictive to response to ICI. However, the microtumoral environment has immunosuppressive attributes, with immunosuppressive M2 macrophages, overexpression of indoleamine 2,3-dioxygenase (IDO) or PD-L1, and loss of major histocompatibility complex type 1. In addition to inhibiting the KIT oncogene, imatinib appears to act by promoting cytotoxic T-cell activity, interacting with natural killer cells, and inhibiting the expression of PD-L1. Paradoxically, imatinib also appears to induce M2 polarization of macrophages. There have been few immunotherapy trials with anti-CTLA-4 or anti-PD-L1drugs and available clinical data are not very promising. Based on this comprehensive analysis of TME, we believe three immunotherapeutic strategies must be underlined in GIST. First, patients included in clinical trials must be better selected, based on the identified driver mutation (such as PDGFRα D842V mutation), the presence of tertiary lymphoid structures (TLS) or PD-L1 expression. Moreover, innovative immunotherapeutic agents also provide great interest in GIST, and there is a strong rationale for exploring IDO targeting after disease progression during imatinib therapy. Finally and most importantly, there is a strong rationale to combine of c-kit inhibition with immune checkpoint inhibitors.