A Study of Duvelisib in Participants With Relapsed or Refractory Peripheral T-cell Lymphoma (PTCL)

The study had 2 phases, a Dose Optimization Phase and an Expansion Phase. In the Dose Optimization Phase, participants were randomly assigned to 1 of 2 study cohorts, as follows: * Cohort 1: Duvelisib per oral (PO) twice daily (BID) at a starting dose of 25 milligrams (mg), with potential escalation on a per-participant basis to 50 mg and then 75 mg, based on the participant's response to and tolerance of therapy, in 28-day cycles. * Cohort 2: Duvelisib 75 mg PO BID, administered in 28-day cycles. A total of 20 participants were to be enrolled in the Dose Optimization Phase, with 10 participants per cohort. Based on the safety and activity data obtained in the Dose Optimization Phase of the study, the Expansion Phase dose of duvelisib was to be determined. In the Expansion Phase, approximately 100-130 participants were to be enrolled and receive duvelisib dose in 28-day cycles as determined in Dose Optimization Phase.