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Introduction: Targeted therapy using specific inhibitors against tyrosine kinases (TKs) is a paradigm in non-small-cell lung cancer management. However, the success of TK inhibitor (TKI) therapy depends on certain activating or acquired mutations, which render sensitivity or resistance to TKIs in the patients. The acquisition of epidermal growth factor receptor (EGFR) T790M point mutation is the most common mechanism of resistance to TKI in non-small cell lung cancer. A number of molecular strategies are now available for molecular testing of non-small cell lung cancers. However, almost all of them are cost-intensive and laborious and require high-end advanced equipment. Thus, assays that are rapid, simple, and cost-effective, yet sensitive, are most ideal in clinical settings for screening such therapeutically relevant mutations., Materials and Methods: Allele-specific loop-mediated isothermal amplification assay (AS-LAMP), which is a variant of the original LAMP assay, is a promising diagnostic technique for screening single-nucleotide polymorphisms. Using commercially available plasmid constructs as template DNA, AS-LAMP assay for EGFR T790M mutation was optimized with six different sets of reaction mixture containing varying concentrations of buffer and primers. The results of AS-LAMP assay were further validated by ultrasensitive droplet digital polymerase chain reaction., Results: Only one of the six sets of reaction mixture could accurately distinguish between wild type and mutated DNA, indicating that the primers and buffer are the two most critical components that determine the accuracy of AS-LAMP. The optimized AS-LAMP assay was further used to screen germ line and somatic T790M mutations in non-small cell lung cancer using blood and tissue samples collected from patients., Conclusion: Development of an accurate and rapid diagnostic assay that can detect resistant mutations without the need for sequencing is highly useful for clinicians in deciding on the eligibility of patients for TKI therapy. Considering its several inherent advantages, AS-LAMP assay could become an effective molecular tool for screening baseline or acquired EGFR T790M mutations in non-small cell lung cancer patients., Competing Interests: There are no conflicts of interest, (Copyright: © 2020 Journal of Carcinogenesis.)