Background: In April 2020 pembrolizumab, an immune checkpoint inhibitor, received approval by the US Food and Drug Administration for an alternative dosing regimen of 400mg IV every 6-weeks (Q6W) in addition to 200 mg IV every 3-weeks (Q3W) across its multiple oncology indications. This study aims to describe real-world utilization of the Q6W dosing regimen and factors associated with it.

Methods: This retrospective study used the nationwide Flatiron Health electronic health record-derived database. Patients included were ≥18 years old, initiated pembrolizumab from 28 April 2019 (1 year pre-Q6W approval) to 28 February 2021 (data cut-off), as monotherapy in first-line (1L) or second-line/later (2L+), or as combination therapy in 1L for the treatment of either advanced non-small cell lung cancer (aNSCLC) or head and neck squamous cell carcinoma (aHNSCC). Patients were excluded if they had both aNSCLC and aHNSCC. A ‘switch’ was defined as a change in dosing regimen within the same line of therapy. Univariate and multivariate analyses were performed to understand factors associated with initiation of Q6W dosing, including ethnicity, race, regimen type, geographical region, and treatment setting.

Results: 4,488 patients were included, with median age of 70 (range 30–85); 54.9% were men; 91.0% had aNSCLC. 1,747 patients (38.9%) initiated pembrolizumab during the post-approval period, while 2,741 patients (61.1%) initiated during pre-approval period. In the post-approval cohort, 145(8.3%) patients initiated pembrolizumab therapy with Q6W with an additional 46(2.6%) patients who switched to Q6W after initiating Q3W during post-approval. In the pre-approval cohort, 135(4.9%) patients switched from Q3W to Q6W dosing regimen once approved. Initiation of the Q6W dosage was more likely with pembrolizumab monotherapy [RR 2.0(95%CI 1.5-2.7)] and in Caucasian patients [RR 2.1(95% CI 1.4-3.1)].

Conclusions: This study describes the utilization of Q6W pembrolizumab Q6W dosing since approval in the US and helps understand the factor associated with it.