Patients and Study Design
Patients aged ≥ 18 years were recruited from 15 hospitals in China into this confirmatory, Phase III, single-arm, open-label study, which was conducted between September 2015 and July 2017 (ClinicalTrials.gov identifier: NCT03349333). Enrolled patients had PTCL (World Health Organization disease classification [23]), which included PTCL NOS, AITL, ALCL (anaplastic lymphoma kinase [ALK] + or −), ENKTL nasal type, EATL, hepatosplenic T-cell lymphoma, subcutaneous panniculitis-like T-cell lymphoma, ATL (human T-cell leukemia virus +), aggressive NK-cell leukemia, and transformed mycoses fungoides disease subtypes, which were confirmed by central pathology review. In addition, patients had disease progression after one or more prior systemic therapy and an enlarged lymph node or extranodal mass (> 1.5 cm). Patients were also required to have Eastern Cooperative Oncology Group Performance Status (ECOG PS) ≤ 2, no brain metastases, and adequate hematological, renal, and hepatic function (absolute neutrophil count ≥ 1000/µl; platelet count ≥ 100,000/µl; total bilirubin ≤ 1.5 mg/dl; aspartate aminotransferase and alanine aminotransferase ≤ 2.5 × upper limit of normal [ULN, or < 5 × ULN if hepatic involvement with lymphoma], and creatinine clearance ≥ 50 ml/min [or creatinine ≤ 1.5 mg/dl]). Exclusion criteria included use of investigational drugs or biologics within 4 weeks of study start, prior allogenic hematopoietic stem cell transplantation (or autologous hematopoietic stem cell transplantation ≤ 100 days of study start), and congestive heart failure, uncontrolled infection, unstable cardiac disease, or other serious illness deemed to impair adherence to study treatment.
Eligible patients received pralatrexate 30 mg/m2 intravenously (IV) administered weekly in 7-week cycles (6 weeks on treatment, 1 week off treatment), along with vitamin B12 (intramuscularly (IM), administered every 8–10 weeks) and folic acid (orally (PO), 1.2 mg/day), which were initiated ≥ 10 days prior to study treatment. Pralatrexate was continued for 24 months or until disease progression, treatment intolerance, investigator decision, or withdrawal of consent, and a safety follow-up was conducted for 24 months following the last dose of study medication. Dose reductions and interruptions were permitted for adverse events (AEs). However, patients were discontinued from the study if three or more sequential doses of pralatrexate were omitted due to treatment-related AEs or if there was a ≥ 3-week lapse between pralatrexate doses.
Supportive-care medications were permitted during the study, including antiemetic therapy and hematopoietic growth factors (excluding pegfilgrastim). Additional therapies for T-cell lymphoma including radiotherapy, cytotoxic or biologic agents, and immunomodulators were not permitted.
The study protocol was approved by the Ethics Committees at each institution, and the study was conducted in accordance with the Declaration of Helsinki, International Conference on Harmonization Guidelines for Good Clinical Practice and China Good Clinical Practice guidelines. All patients provided written informed consent.
Study Endpoints and Assessments
The primary endpoint was ORR, assessed per International Working Criteria [24], and defined as the proportion of patients achieving complete response (CR), unconfirmed complete response (CRu), or partial response (PR) as their best overall response per central, independent review. Radiological response was assessed ≤ 7 days prior to the first dose in Cycles 2–4, alternate cycles thereafter, and when disease progression was suspected (investigator-assessed response was a supportive analysis). Pre-specified subgroup analyses of ORR included age, gender, PTCL subtype per investigator review, best response to any prior treatment for PTCL, best response to most recent prior treatment for PTCL, number of prior systemic regimens, time from most recent therapy, and baseline LDH level. Post hoc subgroup analyses included the PCTL subgroup from the central review and prior CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) exposure.
Secondary endpoints included duration of response (DoR), time to response (TTR), progression-free survival (PFS), and overall survival (OS). Safety was assessed by regular monitoring of AEs (National Cancer Institute Common Terminology Criteria for AEs [NCI CTCAE] version 4.03), hematology, blood chemistry, and vital signs. Pharmacokinetic parameters, including area under the concentration-time curve (AUC), maximum concentration (Cmax), clearance, half-life (t1/2), and volume of distribution, were also assessed in a subset of patients (n = 15) using blood samples collected during Cycle 1 (doses 1 and 6: prior to pralatrexate injection and 3, 5, 8, 12, 18, 24, 48, and 72 h post injection; doses 2–5: pre-injection). The two diastereomers of pralatrexate, S-pralatrexate and R-pralatrexate, were assessed at each timepoint using a validated liquid chromatography/mass spectrometry method.
Statistical Analysis
The primary objective was to demonstrate an ORR ≥ 15% and was tested using the exact binomial test for single proportion at a two-sided significance level of 5%. Assuming a true response rate of 29%, 68 patients would be required to provide 80% power. Safety, pharmacokinetic, and TTR data were summarized using descriptive statistics, while PFS and OS were analyzed using Kaplan-Meier methodology. Pharmacokinetics were assessed using a noncompartmental method (Phoenix, WinNonline version 7).
The primary and secondary endpoints were assessed in the safety population (all patients who received one or more doses of pralatrexate).