A Meta-Analysis of Pivotal Pralatrexate Studies in Relapsed/Refractory Mature T-Cell Lymphoma (r/r TCL)

Introduction

While patients with r/r TCL have a poor prognosis, significant progress has been made over the past decade in developing new drugs and regimens for the disease. All of the approved agents have their own distinct advantages and issues, making it essential to critically assess the merits and limitations of each. It is well accepted that the development of acquired drug resistance to conventional chemotherapy reduces efficacy with each subsequent line of therapy. However in the era of novel single agents, less is known about the role of these new drugs in patients with chemo-sensitive and chemo-refractory disease. Based on results of the PROPEL trial in 111 treated patients, pralatrexate was the first drug approved as a novel single agent in the US for r/r TCL (O'Connor et al. J Clin Oncol. 2011). Drug registration and approval of pralatrexate was subsequently attained in many healthcare ministries around the world, including Japan, China and Taiwan based on the results of PROPEL and/or locally conducted studies (Maruyama et al. Cancer Sci 2017; Hong et al. Target Oncol 2019; Wang et al. EHA 2019). A meta-analysis of these four trials was undertaken to better understand those factors influencing efficacy and safety of pralatrexate in this patient population.

Methods

Patient- or summary-level data presented in the individual clinical study reports from the four regulatory-mandated prospective clinical trials of pralatrexate monotherapy in patients with r/r TCL were included in this meta-analysis. Pooled studies (phase 2 PDX-008 [PROPEL], phase 3 FOT12-CN-301, phase 4 FOT14-TW-401, phase 2 part of PDX-JP1) collected data on the primary efficacy endpoint of objective response rate (ORR) as assessed by central review. Secondary efficacy endpoints included duration of response (DOR), progression-free survival (PFS), and overall survival (OS). Data were collected in accordance with the original protocol and updated with longer survival follow-up where available. Relapse was defined as achieving a complete response (CR) or partial response (PR) on prior therapy lasting for > 3 months, and refractory was defined as stable disease or progressive disease on prior therapy or relapsed disease <3 months of achieving CR or PR. Both the fixed effect model (includes within study variations) and random effects model (includes within study and between study variations) were considered in this meta-analysis.

Results

A total of 221 patients were included in the efficacy analysis set for this meta-analysis. The median age was 59 years (range 21-89) and 67% were male. Histological subtypes as assessed by the central review included PTCL-not otherwise specified (108 pts, 49%), angioimmunoblastic T-cell lymphoma (47 pts, 21%), anaplastic large cell lymphoma (ALK-negative; 26 pts, 12%), transformed mycosis fungoides (12 pts, 5%), extranodal NK/T cell lymphoma, nasal type (7 pts, 3%), and other/missing (10/11 pts, 5% each). Patients had a median of 2 prior lines of systemic therapies (range 1-14). At the most recent line of therapy prior to pralatrexate, 68 (31%) and 103 (47%) patients were classified as relapsed and refractory respectively, with the remaining 50 (23%) unable to be determined due to response to the prior therapy being unavailable or not evaluable. Ten percent (n=24) of patients had stem cell transplant prior to receiving pralatrexate. Pooled ORR of the entire cohort was 40.7% (95% CI, 34.2, 47.5), including 30 in CR (13.6%) and 60 in PR (27.2%). The median DOR was 9.1 months (95% CI, 7.4-10.8). Median PFS was 4.6 months (95% CI, 4.0-5.2) while median OS was 16.3 months (95% CI, 13.1-22.6).

Conclusions

This meta-analysis confirms significant clinical activity of pralatrexate in heavily treated patients with r/r TCL, with an ORR of 40.7% at a median of two lines of prior therapy. These findings meaningfully bolster the original observations from PROPEL with 3 additional regulatory mandated clinical studies and suggest that earlier use may be associated with improved outcome. Further details on the efficacy by prior lines of systemic therapy as well as safety data will be presented.