A phase II study of PXD101 (belinostat) in relapsed and refractory aggressive B-cell lymphomas (rel/ref ABCL): SWOG S0520.

Abstract

e18536 Background: The mechanism of action of histone deacetylase inhibitors (HDACI) in lymphomas is unknown. Loss of major histocompatibility Class II antigens (MHC II) in diffuse large B-cell lymphomas (DLBCL) is associated with decreased tumor infiltrating T lymphocytes (TIL) and poor survival. Transcription of MHC II is controlled by CIITA, which is itself regulated by histone acetylation, We hypothesized that PXD101 (belinostat), an HDACI, would increase MHC II expression in tumor cells, enhance immunosurveillance and improve outcome. Methods: Theprimary objective was to evaluate response rate and toxicity of PXD101 in patients (pts) with rel/ref ABCL with up to 5 prior chemotherapy regimens. Secondary objectives were to estimate the 6-month progression-free survival (PFS) and to assess MHC II and TIL. In a two-stage design, if at least 1 response was observed in the first 20 pts, another 20 pts would be accrued. PXD101 was administered at 1000 mg/m2 IV days 1-5 of 21-day cycle for up to 2 years. Results: The study was closed due to lack of response in the first stage. Of 22 pts enrolled, 19 were evaluable. Median age was 69, and median number of prior treatments was 3 (range 1-4). 18 pts had DLBCL and 1 had B-cell lymphoma, unclassifiable. Grade 4 toxicities were fatigue and muscle weakness (1) and lymphopenia (1). Despite initially finding no responses, 2 partial responses (PR) were observed at 5 and 13 months after registration, for an overall response rate (95% CI) of 10.5% (1.3-33.1%); 3 pts had stable disease (SD), lasting 4.7, 30.4+, and 40.7+ months. With a minimum follow-up of 2.0 yrs, median and 6-month PFS are 2.1 months (1.3-3.8) and 21.1% (6.6-41.0%); median and 6-month overall survival are 13.4 months (95% CI not yet estimable) and 57.9% (33.2-76.3%), respectively. Conclusions: Despite early closure, delayed PR was seen in 2 of 19 pts, and 2 pts had SD lasting 30.4+ and 40.7+ months. Therefore 4 pts (21%) who did not achieve complete response, very unusually, have not progressed for ≥2.0 yrs. Standard chemotherapy response assessment may not be appropriate for HDACI, which may require development of new biomarkers of response. Further work focuses on combining HDACI with standard chemotherapy.