Abstract P013

Subcutaneous Pembrolizumab (Pembro) in Relapsed or Refractory Classic Hodgkin Lymphoma (cHL) or Primary Mediastinal Large B-cell Lymphoma (PMBCL): Additional Follow-Up From a Phase 2 Study

Background: Subcutaneous pembro is approved outside the US for treatment of relapsed or refractory (R/R) cHL and PMBCL. Prior analysis of an open-label, phase 2 study (NCT06504394) evaluated pharmacokinetics (PK), efficacy, and safety of subcutaneous pembro in participants (pts) with R/R cHL or R/R PMBCL. At a median follow-up of 2.6 months, subcutaneous pembro 790 mg Q6W had a manageable safety profile and efficacy consistent with intravenous pembro. Additional follow-up are presented that includes complete cycle 1 data for all pts.

Methods: Eligible pts were ≥18 years with histologically confirmed, FDG-avid cHL or PMBCL per WHO criteria, radiographically measurable disease, and ECOG PS 0 or 1. Pts with cHL or PMBCL were anti–PD-1 naive and had disease that was refractory to, did not achieve CR with, or had relapsed after prior therapy. Pts with cHL received ≥1 multiagent regimen, and those with PMBCL received ≥2 prior therapies (including ≥1 rituximab-based regimen). Pts could enroll if they were ineligible for or had relapsed after stem cell transplant. Pts received subcutaneous pembro 790 mg Q6W for ≤18 cycles (~2 years) or until disease progression or other discontinuation criteria were met. Primary objectives included PK exposure measures during cycle 1 (C1) and ORR; secondary objectives included safety and duration of response (DOR). OS and PFS were exploratory objectives. ORR, DOR, and PFS were assessed per Lugano criteria by investigator.

Results: At data cutoff (January 28, 2026), 64 pts had enrolled and received ≥1 cycle of subcutaneous pembro (n=58, cHL; n=6, PMBCL). Median follow-up was 9.9 months (range, 1.4-15.0). PK exposures of subcutaneous pembro in pts with hematologic tumors were consistent with those with IV pembro (table). Overall, 57 pts with cHL and 4 with PMBCL had a baseline and postbaseline assessment. For pts with cHL ORR was 84% (95% CI, 72-93; 26 CR; 22 PR). Among those with PMBCL, the ORR was 75% (95% CI, 19-99; 1 CR and 2 PR). For pts with cHL, median DOR was 8.3 months (range, 0.0+-10.8+), median PFS was 11.0 (95% CI, 8.5-NR) and median OS was NR (95% CI, NR-NR). Among all pts, 12 (19%) had a grade 3 or 4 treatment-related AEs (TRAEs), and 3 (5%) discontinued due to a TRAE. No deaths due to TRAEs occurred.

Conclusion: With ≥9 months follow-up, the PK profile was consistent with the previous report; subcutaneous pembro Q6W continues to demonstrate durable responses with no new safety concerns.