Open-Label Study of Parsaclisib, in Japanese Participants With Relapsed or Refractory Follicular Lymphoma (CITADEL-213)

Inclusion Criteria: * Male or female Japanese participant who must be ≥ 18 years of age * Ability to comprehend and willingness to sign a written ICF and comply with all study visits and procedures * Histologically confirmed, relapsed or refractory, FL Grade 1, 2, and 3a * Ineligible for HSCT * Must have been treated with at least 2 prior systemic therapies for FL * Radiographically measurable lymphadenopathy or extranodal lymphoid malignancy (defined as the presence of ≥ 1 lesion that measures \> 1.5 cm in the LD and ≥ 1.0 cm in the LPD, respectively) as assessed by CT or MRI * Participants must be willing to undergo an incisional, excisional, or core needle lymph node or tissue biopsy or provide a lymph node or tissue biopsy collected after the completion of last therapy. An earlier archived lymph node or tissue biopsy is acceptable if hospitalization is required for biopsy (eg. no superficial lymph node) and SUVmax by FDG-PET is \< 14 * ECOG performance status 0 to 2 * Life expectancy ≥ 12 weeks * Adequate hematologic, hepatic, and renal functions ANC ≥ 1.0 × 109/L Hemoglobin ≥ 8.0 g/dL. Platelet count ≥ 50 × 109/L. Total bilirubin ≤ 1.5 × ULN. Participants with documented history of Gilbert's syndrome and in whom total bilirubin elevations are accompanied by elevated indirect bilirubin are eligible. ALT/AST ≤ 2.5× ULN or ≤ 5 × ULN in the presence of liver involvement. Calculated creatinine clearance ≥ 40 mL/min by the Cockcroft-Gault Equation or the estimated glomerular filtration rate ≥ 40 mL/min/1.73 m2 using the Modification of Diet in Renal Disease formula. * Female participants agree to use medically acceptable contraceptive measures, should not be breastfeeding, and must have a negative pregnancy test before the start of study drug administration. * Female participants of childbearing potential must understand and accept that pregnancy must be avoided during participation in the study. * Male participants should avoid fathering children from screening through at least 93 days after the last dose of study treatment. Exclusion Criteria: * Known histological transformation from indolent NHL to DLBCL * History of central nervous system lymphoma (either primary or metastatic) * Prior treatment with the following: 1. Selective PI3Kδ or pan-PI3K inhibitors (eg, idelalisib, copanlisib, duvelisib, etc). 2. Bruton's tyrosine kinase inhibitor (eg, ibrutinib). * Allogeneic SCT within the last 6 months, or autologous SCT within the last 3 months before the date of study treatment administration * Active graft-versus-host disease * Use of immunosuppressive therapy within 28 days of the date of study treatment administration * Concurrent anticancer therapy * Significant concurrent, uncontrolled medical condition including, but not limited to, renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, neurological, cerebral, or psychiatric disease * Current or previous other malignancy within 3 years of study entry, except cured basal or squamous cell skin cancer, superficial bladder cancer, prostate intraepithelial neoplasm, carcinoma in situ of the cervix, or other noninvasive or indolent malignancy without sponsor approval. * Hepatitis B (HBV) or HCV infection * Current New York Heart Association Class II to IV congestive heart failure or uncontrolled arrhythmia