Background and Importance Pembrolizumab is an anti-PDL-1 monoclonal antibody widely used in a variety of tumoural diseases. Initially used in a fixed-dose regime, trials showed that a weight-based dosing was more cost-effective and thus it was authorised by the Pharmacy Committee in our centre.

Aim and Objectives To compare the effectiveness of pembrolizumab, either as a fixed 200 mg dose or as a weight based 2 mg/kg dose every three weeks, in combination with pemetrexed and platinum, used in the first line setting as treatment of non-squamous non-small-cell lung cancer (NSCLC), with a CPS count <50%. In addition, to evaluate the economic impact of this dosing change.

Material and Methods Retrospective, observational, descriptive study of all patients treated with pembrolizumab, pemetrexed and platinum in non-squamous NSCLC between January 2018-August 2022. Collected variables: age, sex, weight, dosing, number of cycles, best response, progresion-free survival (PFS), overall survival (OS). Actual cost was calculated accounting for each patient, cycle and milligram of pembrolizumab administered.

Results Forty-six patients (38 men and 8 women), with a median of 65 years old (range 39-77) were included. 26 patients (57%) received a weight based, 2 mg/kg dose (WD group). The median body weight was 73 kg in both groups (range 49-105). Overall response rate (complete/partial response) was 60% in the WD and 50% in the FD group. PFS was 13.24 months (CI95% 10-16.5) on average in the WD group and 13.7 months (CI95% 8.1-19.1) in the FD group. OS was 18.15 months (CI95% 14.3-22) in the WD group and 18.16 (CI95% 12.6-23.6) in the FD group. No significant differences were found in the log-rank test.

Patients in the WD group received an average of 148 ± 27 mg of pembrolizumab for a median of 22 cycles; the FD group received 200 mg and a median of 41 cycles. Most patients (95%) received a lower dose than those in the FD group. On average, the total treatment cost per patient was reduced by 34% in the WD group. The estimated saved public expenditure was €420852 in this pathology.

Conclusion and Relevance Pembrolizumab weight-based dosing was as effective as the fixed dose regime and reduced costs in patients with NSCLC.

Conflict of Interest No conflict of interest