Background: Constitutive activation of the JAK-STAT pathway has been reported in lymphomas, suggesting that targeting this pathway could show clinical benefit. Ruxolitinib phosphate, an oral JAK inhibitor represents a potential therapeutic agent for high grade lymphomas. This study is designed to investigate benefits of ruxolitinib in patients with relapsed or refractory PTCL and DLBCL Methods: Patients with relapsed/refractory DLBCL and aggressive T cell lymphomas who were ineligible for, or relapsed after, stem cell transplantation were eligible. Patients received ruxolitinib, at a dose of 10mg or 5mg BID, with gradual escalation to 25mg BID. Weekly hematological assessments were done during the first cycle, CT scans were done after every two cycles. Descriptive statistics for response to therapy were collected. Progression free survival (PFS), Overall survival (OS) curves were plotted using Kaplan-Meier method, comparisons between groups were made using the log rank test. Primary outcome of the study was to assess the overall response rate (ORR). Secondary objectives were to determine PFS, OS, duration of response and safety. Relationship between responses to oral ruxolitnib and gene expression profiling was explored. Results: Of the 60 patients enrolled, 25 patients had PTCL, 32 DLBCL, 3 pending path review. Median age was 62 yrs., 56.6% had stage IV disease. Median number of cycles received was 2 (min 1, max 60). At the time of evaluation, 76% patients had progressed on therapy. The median follow-up of patients was 3.7 months (min 0.9; max 61.4). Data for 41 patients was available for evaluation of response. Complete response (CR) was noted in 1 patient with PTCL. Partial response (PR) was noted in 1, stable disease (SD) in 4 patients. Among the responders, a PTCL patient with SD had a sustained response for 60 months, a patient with PR had a response duration of 31 months. The median OS and PFS were 5.9 and 1.8 months. PFS was 2.2 months in patients with PTCL and 1.8 months in DLBCL. Median OS was 5 months in patients with DLBCL, 6.9 months in PTCL. The estimated 6 month PFS and OS were 17% (95%CI: 9%, 28%) , 49% (95%CI: 35%, 62%). There was no difference in PFS or OS between PTCL and DLBCL (p = 0.42, p = 0.94). Grade 3 or higher adverse events were seen in 62%. Anemia was seen in 20%, thrombocytopenia in 8%, infections in 6%. Conclusions: Ruxolitinib can produce responses in some patients with relapsed/refractory NHL, particularly in patients with PTCL. It may play a role in combination therapies in future. Clinical trial information: NCT01431209