Optimizing lazertinib therapy through GSTM1 genotyping: a strategy to reduce excess drug exposure and potential toxicity

PURPOSE: The combination of lazertinib and amivantamab has shown superior efficacy over first line osimertinib in EGFR-mutated metastatic non-small cell lung cancer, but is associated with significant toxicity and high costs. Lazertinib exposure varies widely due to genetic polymorphisms of the encoding for GSTM1, with almost 50% of Caucasians having a non-functional enzyme resulting in an approximate twofold higher systemic drug exposure. Despite this, all patients receive a fixed 240 mg once-daily dose irrespective of GSTM1 status, leading to avoidable toxicity without additional clinical benefit. Our purpose was to develop alternative dosing regimens based on GSTM1 status.

METHODS: We conducted pharmacokinetic simulations using an existing validated population pharmacokinetic model to evaluate genotype-guided alternative dosing strategies in GSTM1 null individuals.

RESULTS: Two regimens- 160 mg once daily (QD) and 240 mg every other day-were predicted to provide systemic exposures comparable to or exceeding those seen in GSTM1 non-null patients on the standard dose. The 160 mg QD dose resulted in a geometric mean ratio in GSTM1 null patients (GMR) for the trough (Ctrough) and average (Caverage) concentration relative tot he approved dose in GSTM1 non-null patients of 1.43 and 1.19, respectively. The respective GMRs for Ctrough and Caverage associated with 240 mg every-other-day dosing were 0.90 and 0.89, and this dosing regimen could reduce drug expenses up to 50% ($132.860 per year per patient) based on current pricing.

CONCLUSION: Our findings support the feasibility of individualized lazertinib dosing based on GSTM1 status to reduce toxicity and healthcare costs without compromising effective exposure.