Citations

Abstract Idiopathic HES is a myeloproliferative disorder (MPD) characterized by persistent overproduction of eosinophils resulting in organ damage. In a small subset of patients (pts), the disease is caused by the FIP1L1-PDGFR-α fusion tyrosine kinase. Its expression has been associated with complete clinical responses to therapy with tyrosine kinase inhibitor (TKI) imatinib mesylate. In contrast, there is no specific therapy for pts with HES lacking FIP1L1-PDGFR-α expression and corticosteroids are used for palliation. Alemtuzumab (Campath-1H™) is a humanized rat monoclonal antibody directed against the CD52 antigen. Since CD52 is expressed on eosinophils, we evaluated its efficacy in pts with FIP1L1-PDGFR-α-negative symptomatic HES. A total of 9 pts (5 male, 4 female) received alemtuzumab in weekly cycles at the dose of 30 (8 pts) or 10 (1 pt) mg 3 times a week intravenously or subcutaneously. During the first week alemtuzumab was given in escalating doses (3→10→30mg) to assure tolerance. Median age was 53 years (range 24–70), time from HES diagnosis to alemtuzumab therapy 34 months (range 4–195), median WBC 17×109/L (range 6.9–82.4), absolute eosinophil count (AEC) 9×109/L (range 0.7–30), and bone marrow eosinophils 23% (range 10–68). Three pts had abnormal cytogenetics: del11(q23), +8, and t(5;6). Pts had received a median of 3 prior therapies (range 2–6), including corticosteroids (prednisone; n=9), imatinib (n=7), dasatinib (n=3), interferon-alpha (n=3), hydroxyurea (n=3), nilotinib (n=2), and cladribine (n=2). A total of 121 weekly cycles have been administered (median 13 cycles) thus far. A complete hematologic response (CHR; i.e. AEC normalization) was observed in 8 pts (89%) within 4 weeks of therapy; peripheral blood eosinophils were undetectable in 6 of 8 CHR pts. Follow-up bone marrow specimens were available in 3 pts while in CHR (after a median of 5.5 weekly alemtuzumab cycles) showing complete response in 2 and partial response in 1 pt. In addition, 3 pts that were on prednisone and 2 on hydroxyurea at the start of alemtuzumab discontinued them within 2 weeks into therapy. One pt had a remarkable partial response with reduction of AEC from 47.5 to 1×109/L after 8 weekly cycles of alemtuzumab; this patient was on 3g of hydroxyurea and 80mg of prednisone at the start of alemtuzumab and was able to discontinue hydroxyurea and decrease prednisone to 10mg while on alemtuzumab. Five pts who stopped alemtuzumab experienced relapse after a median time of 3.5 weeks (range, 1 to 10) and 1 relapsed while receiving alemtuzumab after 14 weekly cycles. Three pts are currently on alemtuzumab: 2 receiving 30 mg weekly as maintenance while in CHR after 8+ and 19+ weeks, respectively, and 1 with partial response is receiving 30mg 3 times a week. One relapsed pt was rechallenged with alemtuzumab and normalized AEC again. Alemtuzumab was generally well tolerated. Grade 3–4 drug-related toxicities occurred in 2 pts, 1 with neutropenia and 1 with infusion-related fever, which led to transient and complete alemtuzumab discontinuation, respectively. Two pts experienced CMV reactivation that required therapy. In summary, alemtuzumab was well tolerated and has remarkable activity in pts with FIP1L1-PDGFR-α-negative HES. Different dose schedules of alemtuzumab that include prolonged maintenance therapy are warranted to improve the response duration. Updated clinical results will be presented.

Abstract The FIP1L1-PDGFR-α fusion kinase induces hypereosinophilic syndrome (HES) in a subset of patients (pts). Imatinib is a potent inhibitor of PDGFR-α and has been associated with durable hematologic responses in pts with HES. However, development of kinase domain mutations may hamper TKI activity, underscoring the need for novel agents to prevent or overcome resistance. We evaluated the efficacy of the novel TKI EXEL-0862 in FIP1L1-PDGFR-α-expressing cells. In 72-hour MTS assay, EXEL-0862 inhibited EOL-1 cell proliferation with an IC50 of 1.0 nM and markedly decreased phosphorylation of STAT3 and Erk1/2, suggesting inhibition of downstream targets of PDGFR-α. More important, EXEL-0862 induced dose-dependent inhibition of PDGFR-α phosphorylation in peripheral blood mononuclear cells from a pt with HES. Exposure of EOL-1 cells to EXEL-0862 10 nM for 24 hours caused apoptosis as evidenced by flow cytometry (annexin-V/PI staining) and transmission electron microscopy. This was coupled with time-dependent cleavage of caspases-3, caspase-9, and PARP and with mitochondrial damage as reflected by cytochrome c translocation into the cytosol, and a diminished mitochondrial transmembrane potential. Of note, apoptotic features were not evident after 16 hours of EXEL-0862 exposure. Immunoblots showed marked downregulation of Mcl-1, but not of Bcl-2, Bcl-XL, or Bax. To elucidate the mechanism of Mcl-1 cleavage, EOL-1 cells were exposed to 10 nM EXEL-0862 for 6 hours followed by cycloheximide (5 μg/ml), a potent translation inhibitor, which resulted in marked Mcl-1 turnover. Treatment with the proteasome inhibitor MG-132 failed to abrogate EXEL-0862-induced Mcl-1 cleavage, suggesting proteasome-independent degradation. Rather, a decrease of pro-form Mcl-1 (p42) and increase of the cleaved Mcl-1 peptide form of Mcl-1 (p28) coincided with caspase-3 activation. Pretreatment with 20 μM pan-caspase inhibitor Z-VAD abolished EXEL-0862-induced Mcl-1 cleavage, pointing to a caspase--dependent mechanism. Collectively, our results establish EXEL-0862 as a solid candidate for the targeted treatment of pts with FIP1L1-PDGFR-α-positive HES.

Abstract Dasatinib is approved as a second line therapy (Rx) for Philadelphia chromosome (Ph)-positive chronic myeloid leukemia, as it targets Bcr/Abl tyrosine kinase. Due to its activity against other kinases, like KIT and PDGFR, we conducted a Phase II study of dasatinib in patients with Ph-negative acute and chronic myeloid diseases. Sixty-eight patients were treated at the starting dose of 70mg PO BID (9 patients with SM received 140mg as a single dose daily); 4 weeks=1 cycle. All patients were assessed for response and toxicity (no Grade 4 toxicity was observed). The results by disease type are detailed. Systemic mastocytosis: 33 patients were treated (18 indolent, 9 aggressive, 6 with associated hematologic malignancy); median age 57 years (29–74); 14 were males, all PDGFRA−; # prior Rx 1 (0–4), 16 not previously treated; median # cycles 4 (1–20). Two achieved CR: one SM-MF (JAK2 V617F+, complex cytogenetics) and one SM-HES; both c-KIT mutation negative, low tryptase, anemic, failed erythropoietin, and had abnormal WBC differential. SM-MF patient progressed to AML after 8 months on Rx and died, and SM-HES is still in CR after 18+ months. Nine patients had improvement in symptoms related to SM, lasting from 3–18+ months. Nineteen Grade 3 toxicities were observed; dose was reduced to −1 level in 15, and to −2 level in 5 patients. Acute myeloid leukemia: 9 patients were treated; median age 70 years (51–91); 7 were males, 4 had abnormal cytogenetics; # prior Rx 2 (0–3); median # cycles 1 (1–18). CR was observed in an 80y old male with trisomy 8, previously treated with 3+7 chemotherapy with short CR. He relapsed on dasatinib Rx after 60 weeks. Eight patients had no response (4 stopped Rx within first month). Six Grade 3 toxicities were observed. Myelodysplastic syndrome/chronic myelomonocytic leukemia: 6 patients were treated (3+3); median age 68 years (51–75); 4 were males, 1 with abnormal cytogenetics; # prior Rx 1.5 (0–5); median # cycles 1 (1–2). No responses were observed (2 stopped Rx within first month); one Grade 3 toxicity was observed. Hypereosinophilic syndrome/chronic eosinophilic leukemia: 8 patients were treated (5+3); median age 58 years (23–75); 5 were males, 3 had abnormal cytogenetics, all PDGFRA-; # prior Rx 1.5 (0–3); median # cycles 3 (1–17). One female patient with HES achieved CR (previously Rx with gleevec without response). She relapsed after 58 weeks while off Rx due to toxicity. Other patients did not respond (1 stopped Rx within first month); 5 Grade 3 toxicities were observed. Polycythemia vera: one patient was treated; 50yr old female, with no prior Rx, had no response after 3 months of dasatinib Rx. Chronic idiopathic myelofibrosis: 11 patients were treated; median age 63 years (47–77); 10 were males, 2 had abnormal cytogenetics; # prior Rx 2 (0–7); median # cycles 6 (1–9). No responses were observed (1 stopped Rx within first month); 4 Grade 3 toxicities were observed. Conclusion: Dasatinib is active in systemic mastocytosis (overall response rate 33%). Updated clinical and molecular results will be presented.

Abstract Background : Myelofibrosis (MF) is characterized by progressive bone marrow dysfunction, extramedullary hematopoiesis, massive splenomegaly, elevated levels of inflammatory cytokines, severe constitutional symptoms, cachexia and premature death. INCB018424 is a potent, selective inhibitor of JAK 1 and 2 which has demonstrated impressive clinical activity in the early portion of a phase 1/2 study in patients with PMF and Post-PV/ET MF. Methods : Following the initial dose escalation phase with a BID schedule (N=11), both twice daily (10 mg BID to 25 mg BID, N=56) and once daily (25 mg QD to 200 mg QD, N= 37) dose regimens were explored. Endpoints included spleen size assessed by manual palpation, constitutional symptoms assessed using the Modified Myelofibrosis Symptom Assessment Form (MFSAF) and JAK2 allele burden. Exercise capacity is being assessed using the Six Minute Walk Test (6MWT), and body mass and composition are being assessed using standard methods. Safety was assessed by collection of adverse events and monitoring of laboratory data. Results : Over 100 patients are currently enrolled in the study, with a mean exposure to drug of > 5 months. Twenty percent of patients have received INCB018424 for > 9 months. INCB018424 is associated with a rapid reduction of splenomegaly in over 93% of patients from a mean baseline spleen size >20 cm, with 50% or greater reduction being observed in 35% of patients dosed with 10 mg BID or 50 mg QD, and 59% of patients dosed with 25mg BID regimens. These declines nearly always occur within the first month of therapy, with further, slower decreases often observed thereafter. In responding patients, spleen size reduction persists for the duration of therapy (currently up to one year follow-up). Constitutional symptoms are reported with high frequency in the study population as assessed by the MFSAF: night sweats, pruritis and fatigue were reported by >60%, >45% and >90% of patients respectively. Improvements in self-assessed symptom scores (mean % improvement of 40% to 60%) occurred by the first assessment at week 2. Activity limitations are also reported by a high proportion of MF patients; 70% of respondents reported impaired ability to exercise or get around, with a mean score >5 on the 11-point MFSAF scale; INCB018424 therapy was associated with rapid (within 2 weeks) and marked (40% or more) improvement in self-assessed score. There was a dose-dependent weight gain, most pronounced in patients with the lowest body mass index (BMI) values at baseline. Profound reductions in inflammatory cytokines were observed by the first evaluation at week 2 in virtually all patients, and were maintained during therapy. INCB018424 is generally well tolerated with the primary toxicity being dose-dependent grade 3 or 4 reversible thrombocytopenia which occurred in 0%, 18% and 32% of patients dosed with 10 mg BID, 50 mg QD or 25 mg BID. Conclusions : INCB18424 shows unprecedented and durable clinical efficacy in reducing spleen size and improving constitutional symptoms in patients with MF. Results from proactive dose modification regimens, assessments of exercise capacity, MRI-based spleen volume assessment and body composition determination will be presented.

TPS6641 Background: Hydroxyurea is widely used to treat patients with high-risk PV and ET. However, some patients are either clinically resistant to hydroxyurea or have unacceptable side effects, supporting the need for active therapeutic options in this setting. SAR302503 is an orally administered selective JAK-2 inhibitor that reduced symptom burden and provided a durable clinical benefit, including a reduction in the JAK2V617F allele burden, with an acceptable safety profile in a Phase 1/2 trial of patients with primary myelofibrosis (MF), post-PV MF, or post-ET MF (J Clin Oncol 2011;29:789; Pardanani, ASH 2011; Abs 3838). Based on the results in MF, in October 2011 we initiated a Phase 2 trial to evaluate SAR302503 for the treatment of patients with PV and ET who are resistant or intolerant to hydroxyurea (NCT01420783; ARD12042). Methods: Eligibility criteria include age of at least 18 years, ECOG PS 0–2, and hydroxyurea resistant PV or ET as defined by European LeukemiaNet Consensus Criteria (Blood 2009;113:4829). Patients are being randomized (1:1:1) to receive 100, 200, or 400 mg of SAR302503 orally once daily in consecutive 28-day cycles for at least 8 cycles in the absence of progression or unacceptable toxicity. The primary end points will be assessed after the completion of 8 cycles and are: for PV, the proportion of patients maintaining a hematocrit below 45% without phlebotomy for at least 3 months; for ET, the proportion of patients with a platelet count lower than 400 × 109/L for at least 3 months. Secondary objectives include safety, response rate, pharmacokinetics, pharmacodynamics as measured by JAK2V617F allele burden and STAT3 phosphorylation inhibition, assessment of disease-related symptoms, and quality of life. Enrollment of the planned total of 90 patients is ongoing at approximately 45 sites globally. Twelve patients have been enrolled as of January 2012.

TPS6639 Background: SAR302503 is an orally administered selective JAK-2 inhibitor being evaluated for the treatment of MF. In a phase 1 study, SAR302503 reduced spleen size and disease-related symptoms and provided clinical benefit, including a reduction in the JAK2V617F allele burden, with an acceptable safety profile in patients with primary MF, post-PV MF, or post-ET MF (J Clin Oncol 2011;29:789). An ongoing open-label extension of this trial confirmed the durability of those results and found that doses between 400–500 mg/day of SAR302503 represented the optimal balance between safety and efficacy (Pardanani, ASH 2011;Abs 3838). These results led us to initiate a Phase 3 trial in December 2011 to evaluate SAR302503 at doses of 400 mg/day and 500 mg/day, compared with placebo, for the treatment of patients with MF (NCT01437787; EFC12153). Methods: Eligibility criteria include age of at least 18 years, platelets >50,000/µl, ECOG PS 0–2, and a diagnosis of high- or intermediate-risk 2 primary MF, post-PV MF, or post-ET MF according to IPSS criteria (Blood 2009;113:2895). Patients are being randomized (1:1:1) to receive 400 mg or 500 mg of SAR302503 or placebo orally once a day for at least 6 consecutive 28-day cycles. Assigned treatment will continue as long as patients are deriving benefit or until progression or unacceptable toxicity. Cross-over is allowed after 6 cycles or in case of progression before completion of 6 cycles according to predefined criteria. The primary endpoint is spleen response (≥35% reduction in spleen volume by MRI/CT at the end of cycle 6). Key secondary objectives are symptom response rate and durability of spleen response. Additional secondary endpoints include assessment of allele burden and bone marrow fibrosis reduction. It is planned to randomize 75 patients per treatment group at approximately 130 sites worldwide.

Abstract FMS-like tyrosine kinase 3 internal tandem duplications (FLT3-ITD) in acute myeloid leukemia (AML) are associated with early relapse after standard chemotherapy and poor survival. Quizartinib (AC220) is an oral FLT3 receptor tyrosine kinase inhibitor that has shown the highest level of single agent activity seen with a FLT3 targeted agent in FLT3+ relapsed AML to date. This Phase 1 dose escalation study is the first study to report data with quizartinib in combination with standard induction and consolidation chemotherapy in patients aged 18-60 years with newly diagnosed AML, regardless of FLT3-ITD status. The dose escalation was conducted using a modified 3+3 design, where 6 pts were enrolled at each dose level. The pts were given cytarabine 200 mg/m2 x 7 days and daunorubicin 60 mg/m2 x 3 days (7+3) for induction and high dose cytarabine 3 g/m2(HiDAC) q12hours on days 1, 3, and 5 for consolidation. Quizartinib was administered daily for either 7 or 14 days, starting at Day 4 of induction and/or consolidation chemotherapy. Patients were allowed to proceed directly to a stem cell transplant after achieving a response or receive further quizartinib as maintenance therapy after consolidation if they were not transplant eligible. Three dose levels were tested; dose level 1 (DL1) at 60 mg for 7 days, dose level 2 (DL2) 60 mg for 14 days, and dose level -1 (DL-1), 40 mg for 14 days. Through May 31, 2013 18 pts were enrolled in the study, and the safety information at all 3 dose levels are presented. The median age of pts was 43 years (range 22 to 60). Of the 18 patients, 16 had the FLT-ITD mutation. At DL1, one of the 6 patients had a DLT (grade 3 hyponatremia). At DL2, two of the 6 patients had a DLT (grade 3 QTc prolongation and grade 4 pericarditis) which exceeded the pre-specified criteria so DL-1 was then explored. At DL-1, one of the 6 patients had a DLT (grade 3 constrictive pericarditis). The most common (20%) treatment-related adverse events (AEs) were nausea (42%), diarrhea (32%), anemia (26%), febrile neutropenia (26%), neutropenia (21%), fatigue (21%), pyrexia (21%) and thrombocytopenia (21%). The most common (10%) Grade 3 or 4 treatment-related AEs were febrile neutropenia (26%), thrombocytopenia (21%) anemia (21%)), neutropenia (21%), leucopenia (16%), and nausea (11%). The data from this Phase 1 study demonstrates for the first time that quizartinib can be safely administered with induction and/or consolidation chemotherapy in newly diagnosed younger patients with AML. The MTD was identified as 40 mg for 14 days or 60 mg for 7 days. The efficacy results from this Phase 1 study will be available at the time of presentation. Based on these findings, multiple Phase 3 studies in newly diagnosed AML patients are planned. Disclosures: Altman: Novartis: Consultancy; Araid: Consultancy; BMS: Consultancy; Teva: Consultancy; Astellas: Consultancy. Foran:Astellas: Research Funding. Trone:Ambit: Employment. Gammon:Ambit: Employment. Cortes:Ambit: Research Funding.

Abstract Background: A mutation in the Janus tyrosine kinase 2 gene (JAK2 V617F) has been recognized in Philadelphia chromosome-negative myeloproliferative disorders, including PV (∼95% of patients), ET (∼50%) and PMF (∼50%). INCB018424 is a potent and orally bioavailable selective JAK2 inhibitor with >80-fold selectivity against a broad panel of kinases, including JAK3. INCB018424 potently inhibits JAK2 V617F mediated signaling and malignant cell survival in vitro and in vivo in mice. Preclinical safety studies with INCB018424 demonstrated an excellent safety profile with no off-target toxicities. Methods: A phase I/II trial of INCB018424 given orally BID is being conducted in patients with PMF and Post-PV/ET MF. Both JAK2 V617F and JAK2 wild type patients are eligible. PK and PD data are being collected. Responses are being evaluated using the International Working Group (IWG) consensus criteria for treatment response in myelofibrosis with myeloid metaplasia, for the IWG for Myelofibrosis Research and Treatment (IWG-MRT) (Tefferi et al., Blood, 108, 1497–1503, 2006). Results: The initial dose of 25 mg PO BID resulted in a rapid and marked reduction in splenomegaly. All 3 patients in the first cohort of patients achieved a reduction in spleen size that is consistent with a clinical improvement response provided it is sustained for 8 weeks; spleen sizes of 25, 22, and 7 cm below the left costal margin have decreased to 8, 10, and 0 cm in the first month of therapy. At two months follow-up, the patient with a baseline spleen size of 22 cm is now down to 2 cm. All 3 patients also noted significant symptomatic improvement. The second cohort of 3 patients started therapy at an increased dose (50 mg PO BID) and at one week follow-up, the initial two patients (one JAK2 wild type, one JAK2 V617F) had decreases in spleen size from 22 cm to 17 cm and from 22 cm to 16 cm, respectively. No dose-limiting toxicities or other significant adverse events occurred in any patients to date. PK/PD analyses demonstrated that administration of INCB018424 resulted in plasma drug concentrations sufficient to markedly inhibit JAK2, as shown by suppression of phosphorylated STAT3 (a substrate of JAK2) in whole blood cells in all 3 patients in the first cohort. The 3 patients in the first cohort were all JAK2 V617F mutation positive: percentages of JAK2 V617F positive whole blood cells before therapy were 79%, 49% and 91%, and after one month of therapy, they were 59%, 48% and 78%, respectively. Conclusions: Initial results show marked reduction in splenomegaly and symptomatic improvement, without significant toxicity. The percentage of blood cells with JAK2 V617F mutation appears to be decreasing in patients on therapy. Updated results on current and future patients will be presented at the meeting.

Abstract Abstract 3917 Poster Board III-853 Background Patients with Myelofibrosis (MF) suffer from significant fatigue, constitutional symptoms and splenomegaly (Mesa et. al. Cancer 2007) not improved by current therapy. The MF-SAF is a 19 item self administered instrument specific to MF associated symptoms previously validated for use at a single time point (Mesa et. al. Leukemia Research 2009). We sought to assess the performance characteristics of the MF-SAF when administered sequentially in the context of a prospective clinical trial. Methods Sequential MF patients enrolled in the prospective, uncontrolled Phase II, trial were given a 15 item modified MF-SAF to complete at enrollment, and after 15 days, 1 month, 2 months, 3 months and every 3 months thereafter. The MF-SAF was scored as previously published on a 0 (absent) to 10 (maximal) scale. Cross validation of serial change in MF-SAF scores was undertaken by comparison to objective measurements made as part of the therapeutic drug trial. Results Patients Eighty six MF patients were enrolled and had 2 or more MF-SAF instruments completed to allow for sequential analysis. Patients were of a median age (65 years), gender distribution (35 % females), and disease subtype (53 % PMF) typical for a clinical trial in MF. Baseline MF-SAF Responses: Baseline assessment of the most frequent MF abnormalities reported by patients completing the MF-SAF (see Table 1) confirmed the wide prevalence of MF associated symptoms, and their significant severity. General fatigue was the most frequent symptom cited (91%), while cough was the least frequently observed symptom (44%). 95% of patients had at least 2 symptoms present on the MF-SAF. Serial MF-SAF Changes in Response to Therapy Therapy with INCB018424 resulted in a significant and rapid reduction in MF associated symptoms with 46% to 85% of patients experiencing improvement in a given symptom. The greatest improvements in MFSAF score improvements were reported by patients experiencing abdominal discomfort, night sweats, pruritus and fever (see Table 1), and corresponded to significant improvements in the individual MF symptom scales as well as the patient's overall assessment of quality of life (QOL). Correlation of MF-SAF to Objective Changes during INCB018424 Therapy Objective measurements obtained on the INCB018424 trial included MRI measurements of splenic reduction, the six minute walk test (6MWT) for inactivity, and serial weights. Reduction in spleen size (by ≥ 35% by volume or ≥ 50% by palpable length) corresponded to improvement in MF-SAF scores of abdominal discomfort and fatigue (50% of patients, median score decrease of -1.2, and -1.8, respectively). Improvement in the 6MWT by > 50 meters was associated with a 2-fold greater improvement in inactivity score on the MF-SAF compared to subjects who improved 6MWT performance by <50 meters. Finally, improvements in weight loss and fever were corroborated by objective measurements made at physician visits on the trial. Conclusions The MF-SAF is a brief, easily self administered, MF specific instrument which was successfully administered sequentially in the conduct of a large Phase II clinical trial. The significant symptomatic improvements reported by patients in the open label trial of INCB018424 corresponded to both improvements in symptom specific scores on the MF-SAF and objective measurements. Further validation of the MF-SAF will be possible by inclusion in upcoming randomized placebo controlled trials in MF patients. Parallel trials performed in MF patients should consider use of this instrument to allow for comparisons. Disclosures: Levy: Incyte Corporation: Employment, Equity Ownership. Vaddi:Incyte Corporation: Employment, Equity Ownership. Erickson-Viitanen:Incyte Corporation: Employment, Equity Ownership. Verstovsek:Incyte: Research Funding.

Abstract Prompted by the activity of lenalidomide (Revlimid®) in pts with chronic idiopathic myelofibrosis (CIMF), we sought to evaluate the safety and efficacy of the combination of lenalidomide and prednisone in a phase II study for pts with CIMF. The rationale for this combination is that the anti-angiogenic and anti-TNFa effects of lenalidomide may be potentiated by the effects of prednisone to reduce marrow fibrosis and improve hematopoiesis in CIMF. Initial therapy consisted of lenalidomide 10 mg/d (dose level [DL] 0) on days 1–21 of a 28–day cycle for 6 cycles, in combination with prednisone 30 mg/d orally during cycle 1, 15 mg/d orally during cycle 2, and 15 mg/d every other day during cycle 3. The lenalidomide dose could be reduced to 5 mg/d (DL -1) or to 5 mg/d every other day (DL -2), or increased to 15 mg/d (DL +1) or 20 mg/d (DL +2) depending upon toxicity or lack of response, respectively. A total of 40 pts (23 male, 17 female) have been enrolled. The median age was 62 years (range, 41–86), time from CIMF diagnosis to the study treatment 10 months (range, 0–269), WBC count 87x109/L (range, 1.1–89), hemoglobin 9.8 g/dL (range, 7.8–17.3), platelets 137x109/L (range, 8–1183). Pts had received a median of 1 prior therapy (range 0–4): hydroxyurea (HU; n=14), anagrelide (AG; n=4), azacitidine (n=6), steroids (n=5), thalidomide (n=4), and interferon (n=3). Ten (25%) pts had not received any prior therapy. JAK2 V617F mutation was detected in 18 (50%) of 36 tested pts and 20 (50%) of 40 had abnormal cytogenetics. A total of 260 cycles have been administered. All 40 pts are evaluable for response and toxicity. Responses have been observed in 12 (30%) pts, including complete response (CR) in 2 (normal blood counts and <5% bone marrow blasts, off HU, AG, growth factors, and no transfusions); partial response (PR) in 7 (at least 2 of the following: Hb increase by ≥2 g/dL, 50% increase in platelets, decrease of bone marrow blasts or organomegaly by ≥50%, normalization of WBC count without blasts, or reduction in bone marrow fibrosis; off HU, AG, growth factors, and transfusion independence); and hematologic improvement (HI) in 3 (at least 2 of the following: decrease by ≥25% of pretreatment leukocytosis, splenomegaly, or marrow blasts, or increase of Hb by ≥1g/dl without growth factor or transfusion support or platelets by ≥25%; off HU, AG, growth factors). Median time to response was 12 weeks (range, 2–32). Responses have been sustained for a median of 15 wks (range, 5–36) and are ongoing in all 12 responders. Overall, 21 (53%) pts experienced grade 3–4 toxicity, being the most frequent neutropenia, anemia, musculoskeletal pain, and fatigue. Twenty-four (60%) pts have required dose reduction to DL -1, of which 5 (12.5%) further reduced to DL -2. One (2.5%) pt dose-escalated to DL +1, while 15 (25%) remained at DL 0. Twenty-one (53%) pts discontinued lenalidomide due to: lack of response (n=8), pt’s decision (n=7), grade 3–4 toxicity (n=5), and poor compliance (n=1). No deaths or transformation to acute myeloid leukemia occurred. In summary, the combination of lenalidomide and prednisone is an active and generally well-tolerated regimen for pts with CIMF. Longer follow-up is warranted to evaluate the durability of ongoing responses. Updated results will be presented at the meeting.