Abstract 114 Background: Romidepsin is a potent HDAC inhibitor approved by the FDA for patients (pts) with cutaneous T-cell lymphoma who have received at least 1 prior systemic therapy. Durable clinical benefit and tolerability of romidepsin in pts with recurrent or refractory PTCL have been previously observed in a phase 2 trial conducted by the National Cancer Institute. The aim of this phase 2, single-arm, open-label registration study was to evaluate the activity of romidepsin in a larger number of pts with progressive or relapsed PTCL. Methods: Pts with histologically confirmed PTCL (PTCL NOS, angioimmunoblastic T-cell lymphoma, ALCL [ALK-1 negative], other subtypes) who failed or were refractory to ≥ 1 prior systemic therapy, and had measurable disease and ECOG performance status 0–2 were eligible. Exclusions included inadequate bone marrow or other organ function and significant cardiovascular abnormalities. Pts received romidepsin 14 mg/m2 as a 4-h IV infusion on days 1, 8, and 15 every 28 days for up to 6 cycles; treatment could be extended for stable disease (SD) or response. The primary endpoint was rate of complete response (CR + CRu) as evaluated by a central Independent Review Committee (IRC) using International Working Criteria for non-Hodgkin9s lymphoma. IRC assessment consisted of a 2-step process, with initial radiographic review of images (CT, MRI) followed by an overall clinical assessment based on the radiology evaluations, photographs, and relevant clinical parameters. Secondary endpoints included objective response rate (ORR): CR + CRu + partial response (PR), investigator-assessed responses, duration of response, time to response, and safety. Results: 131 pts from 48 US, European, and Australian sites were enrolled and received at least 1 dose of romidepsin (as-treated population); 130 patients had histologically confirmed PTCL by central review. Mean age of all pts was 59.4 y (range, 20–83) and median time since diagnosis was 1.25 y (range, 0–17). Median number of prior systemic therapies was 2 (range, 1–8). 21 pts (16%) had failed a prior stem cell transplant. Responses assessed by the IRC are noted in the table below. Longest duration of response is 26+ mo and 16 (94%) of the 17 pts with a CR had not progressed as of the data cutoff (March 31, 2010). Investigator-assessed responses included 21 pts (16%) with CR + CRu, 18 pts (14%) with PR for an ORR of 30%. Currently, 13 pts continue to receive treatment (range, 10–36 cycles). Adverse events (AEs) were reported in 126 of 131 pts (96%). AEs reported in ≥ 20% of pts were nausea (59%), fatigue (41%), vomiting (38%), thrombocytopenia (38%), diarrhea (35%), pyrexia (34%), neutropenia (30%), anorexia (28%), constipation (28%), anemia (23%), and dysgeusia (21%). AEs ≥ grade 3 were reported for 86 pts (66%), with the most common (≥ 5%) being pneumonia (5%), pyrexia (5%), sepsis (5%), and vomiting (5%). 60 pts (46%) had at least 1 serious AE: the most frequently reported (≥ 5%) were pyrexia (7%), pneumonia (5%), vomiting (5%), and sepsis (5%). 22 pts (17%) withdrew due to AEs. 8 pts (6%) died within 30 days of the last dose of romidepsin; 1 death, due to sepsis, was assessed as possibly related to treatment. Conclusions: Complete and durable responses were observed with single agent romidepsin in pts with relapsed PTCL. These data support the therapeutic potential for romidepsin in relapsed PTCL and suggest that romidepsin is a strong candidate for inclusion in future novel regimens for these diseases. As of the data cutoff (March 31, 2010), the median duration of follow-up for CR is 8.2 mo. Disclosures: Coiffier:Gloucester: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau. Off Label Use: Romidepsin is indicated for the treatment of cutaneous T-cell lymphoma (CTCL) in patients who have received at least one prior systemic therapy. Romidepsin is not currently approved for the treatment of peripheral T-cell lymphoma (PTCL). Pro:Celgene: Research Funding. Prince:Celgene: Consultancy, Honoraria, Research Funding. Foss:Celgene: Consultancy; Eisai: Consultancy, Speakers Bureau; Merck: Speakers Bureau; Allos: Consultancy, Speakers Bureau; Cephalon: Speakers Bureau. Sokol:Celgene: Membership on an entity9s Board of Directors or advisory committees, Research Funding, Speakers Bureau. Caballero:Celgene: Membership on an entity9s Board of Directors or advisory committees. Morschhauser:Roche: Consultancy, Honoraria; Bayer: Honoraria. Padmanabhan:Celgene: Consultancy, Membership on an entity9s Board of Directors or advisory committees, Research Funding, Speakers Bureau. Shustov:Celgene: Research Funding. Nichols:Celgene: Employment. Carroll:Celgene: Employment. Balser:Gloucester Pharmaceutical: Consultancy. Horwitz:Celgene: Consultancy, Honoraria.