Background: Recurring mutations in epigenetic functions in PTCL, coupled with marked activity of epigenetic drugs, raises a question regarding whether these mutations might portend greater vulnerability to one drug over another. For example, do mutations in genes governing DNA methylation suggest these patients might benefit from a hypomethylating (HMA) agent? Preclinical data from our group suggests marked synergism between histone deacetylase inhibitors (HDACi) and HMA, as well as HDACi and pralatrexate (PDX), irrespective of mutations in epigenetic genes. Phase 1 studies (romidepsin [R] plus PDX or R plus 5-azacytidine [Aza]) are completed, and the Phase 2 studies are near completion. This clinical trial scenario affords a unique opportunity to decipher the impact of a HMA on response as a function of TET2, IDH2, DNMT3 and other mutations in PTCL. Methods: Patients with R/R lymphoma were eligible for the phase 1, whereas the phase 2 only enrolled patients with PTCL, either R/R or treatment-naïve individuals. Exploratory endpoints included next generation sequencing (NGS) and methylation arrays. Results: In toto, 89 patients have been enrolled on both trials across all histology’s, 58 have PTCL. NGS and efficacy data is available for the majority of patients, with some from the PDX + R study in process. The ORR among the PTCL patients for PDX+R and Aza+R has been 71% and 73% respectively. Eight of 9 angioimmunoblastic TCL patients responded. Among those with TET2 mutations, 7 of 8 responded to the Aza based treatment, while only 3 of 6 (50%) who were TET2 negative responded. Similarly, of 3 patients with DNMT3 treated with Aza based therapy, all 3 responded. Remarkably one patient with a TET2 mutation experienced progression to PDX+R, and CR to Aza+R. Among the PTCL patients treated with Aza, the global demethylation score (GDMS) demonstrated marked demethylation among all patients, with no correlation between the score and likelihood of response. Conclusions: We will share the completely annotated analysis correlating clinical metrics to the spectrum of epigenetic mutations and GDMS and across all histology’s and treatments. Clinical trial information: NCT01998035; NCT01947140