B Conclusions: b With approximately 9 mo of follow-up, pembro 400 mg Q6W had robust antitumor activity in pts with R/R cHL and R/R PMBCL, with ORR similar to that with pembro 200 mg Q3W. B Introduction: b Pembrolizumab (pembro) was originally approved by the FDA for the treatment of R/R cHL and R/R PMBCL at 200 mg every 3 weeks (Q3W). Treatment-related AEs occurred in 24 pts (40%) with R/R cHL and 2 (33.3%) with R/R PMBCL; grade >=3 treatment-related AEs occurred in 3 pts (5%) and 1 pt (16.7%), respectively.