Low dose anti-PD(L)-1: A potentially effective alternative for greater accessibility in solid malignancies

e21523 Background: Anti-PD(L)1 agents changed the treatment landscape of multiple tumor types yielding long-term responses in a significant proportion of patients. However, these drugs are costly and not accessible to patients from most countries. Mounting data suggest that lower doses of anti-PD(L)1 can be as efficacious as label-approved doses at lower costs. Herein we compare the outcomes of patients treated with low-dose anti-PD(L)1 agents (LD) and patients treated with conventional doses (CD) at a single tertiary hospital. Methods: This is an observational historical cohort study evaluating the outcomes of patients treated with anti-PD(L)-1 agents (either at LD or CD) at Hospital de Base, São José do Rio Preto - Brazil. We included patients older than 18yo, with solid malignancies and treated with any anti-PD(L)1 agent. Patients were classified as having received LD if the dose administered at the first cycle was below the label dose. Data were abstracted from electronic medical records. Efficacy outcomes, including overall survival (OS), progression-free survival (PFS), and overall response rate (ORR), were evaluated. Log-rank test and Chi-square or Fisher's exact test were used as appropriate. A p-value of 0.05 was considered statistically significant. Results: From January 2020 to October 2022, a total of 43 patients were included: 26 (60.4%) received LD and 17 (39.6%) received CD. The mean age of LD and CD was 66.9 (SD 14.5) and 64.8 (SD 9.7), respectively. Most patients presented with ECOG 0 or 1 (64% LD and 66% CD), had metastatic disease at treatment onset (92% LD and 94.1% CD), and were treated in the first line (50% LD and 64% CD). Most frequent tumor sites were melanoma (38.5% LD, 56.3% CD) and lung (29.9% LD, 18.8% CD). Only 23.1% and 17.6% of tumours in LD and CD were tested for PD-L1 expression, of which 83% and 33% had PD-L1 > 1. Most patients from both groups were treated with pembrolizumab (92.3% LD and 82.4% CD). The mean dose of pembrolizumab was 89.6 mg (1.5 mg/kg) for LD and 171 mg (2.1 mg/kg) for CD. After a median follow-up of 23 months, there was no significant difference in median OS (mOS), mPFS, and ORR between LD and CD (Table). A sensitivity analysis with patients receiving pembrolizumab was performed and had similar results (Table). Conclusions: Our study suggests there is no difference between patients treated with LD and CD anti-PD(L)1 in terms of OS, PFS, and ORR. The numerically shorter OS and PFS in the CD group may be due to selection bias and should be interpreted cautiously. LD anti-PD(L)1 could be an alternative to expand access in places where CD is not affordable. [Table: see text]