PI-034 - ONCOLOGIST CONSIDERATIONS WHEN CHOOSING BETWEEN 200 MG EVERY-3-WEEK VERSUS 400 MG EVERY-6-WEEK DOSING OF PEMBROLIZUMAB MONOTHERAPY WITHIN UPMC HILLMAN CANCER CENTER NETWORK

D. Natesan¹, R. Wong², P. Chablani²; ¹University of Pittsburgh, School of Medicine, Pittsburgh, PA, USA, ²UPMC Hillman Cancer Center, Pittsburgh, PA, USA.

Background: Pembrolizumab (pembro), a common immunotherapy used in cancer treatment, can be given as 200mg every 3 weeks (Q3W) or 400mg every 6 weeks (Q6W). Prior work demonstrated no differences in efficacy or adverse events (AEs) between the two monotherapy doses. Previously, we reported a minority of patients (pts) in the UPMC Hillman Cancer Center network received Q6W dosing (343/1640; 21%), and 36% of those pts started with Q3W before transitioning to Q6W dosing. We now investigate factors influencing oncologist choice of Q3W vs. Q6W dosing.

Methods: An electronic REDCap survey was emailed to oncologists in the UPMC Hillman Cancer Center network, asking about usual choice of pembro monotherapy dosing and factors influencing this decision.

Results: 64/118 (54%) oncologists responded; common specialties were general oncology, genitourinary, and thoracic cancers. 35/64 (55%) reported starting with Q3W and then transitioning to Q6W dosing; 22/64 (34%) use Q3W dosing; 2/64 (3%) use Q6W dosing; and 5/64 (8%) stated that choice of dosing depends on the pt. Oncologists starting with Q3W before transitioning to Q6W dosing cited improved convenience/cost to pt (91%), equivalent safety/efficacy of Q3W vs. Q6W dosing (63%), and reducing the clinic’s treatment volume (26%) as common non-exclusive reasons for transitioning to Q6W dosing. Regarding when to transition, most considered the pt’s AE profile (83%) and treatment response (69%).

Oncologists using Q3W dosing cited the ability to monitor pts more frequently (86%), more familiarity with Q3W dosing (38%), and lower risk of AEs with Q3W dosing (27%). Those using Q6W dosing cited improved convenience/cost to pt (100%). Oncologists who made dosing choices based on the pt largely considered the pt’s travel burden (100%), pt’s preference (80%), and risk of AEs (60%).

36% of oncologists were uncertain or believed that Q6W dosing led to a higher rate or severity of AEs compared to Q3W dosing. One representative comment stated, “Pts for the most part like the 6-week frequency but I have seen anecdotally higher rates of irAE [immune-related AE], possibly more severe.”

Conclusion: Studies report no difference in safety and efficacy between Q3W and Q6W pembro monotherapy. However, most oncologists typically started with Q3W dosing. Additionally, over a third had concerns about the toxicity of Q6W dosing.