Clinical implications of germline variations for treatment outcome and drug resistance for small molecule kinase inhibitors in patients with non-small cell lung cancer

Small-molecule kinase inhibitors (SMKIs) represent the cornerstone in the treatment of non-small cell lung cancer (NSCLC) patients harboring genetic driver mutations. Because of the introduction of SMKIs in the last decades, treatment outcomes have drastically improved. Their treatment efficacy, the development of drug resistance as well as untoward toxicity, all suffer from large patient variability. This variability can be explained, at least in part, by their oral route of administration, which leads to a large inter- and intra-patient variation in bioavailability based on differences in absorption. Additionally, drug-drug and food-drug interactions are frequently reported. These interactions could modulate SMKI efficacy and/or untoward toxicity. Furthermore, the large patient variability could be explained by the presence of germline variations in target receptor domains, metabolizing enzymes, and drug efflux transporters. Knowledge about these predictor variations is crucial for handling SMKIs in clinical practice, and for selecting the most optimal therapy. In the current review, the literature search included all SMKIs registered for locally-advanced and metastatic NSCLC by the US Food and Drug Administration (FDA) or European Medicines Agency (EMA) until March 24th, 2022. The BIM deletion showed a significantly decreased PFS and OS for East-Asian patients treated with gefitinib, and has the potential to be clinically relevant for other SMKIs as well. Furthermore, we expect most relevance from the ABCG2 34 G>A and CYP1A1 variations during erlotinib and gefitinib treatment. Pre-emptive CYP2D6 testing before starting gefitinib treatment can also be considered to prevent severe drug-related toxicity. These and other germline variations are summarized and discussed, in order to provide clear recommendations for clinical practice.