Abstract 503: Longitudinal minimally invasive monitoring of resistance mutations in ALK rearranged lung cancer patients
Authors: Sasaki Takaaki , Hirai Noriko , Minami Yoshinori , Okumura Shunsuke , Chiba Shin-ichi , Yoshida Ryohei 
Published: June 2022

Background: ALK is a proto-oncogene encoding the receptor tyrosine kinase ALK, which can be aberrantly activated by gene rearrangements or point mutations to promote tumor cell growth, survival, and metastasis. ALK rearrangements are detected in approximately 4% of patients with advanced non-small cell lung cancer (NSCLC), and the tyrosine kinase inhibitors (TKIs) crizotinib, alectinib, brigatinib, ceritinib, and lorlatinib have been approved by the FDA for the treatment of ALK-positive NSCLC. The durability of response to these therapies has been limited, in many cases, by the emergence of mutations that confer resistance to ALK. The major resistance mutation to alectinib, brigatinib, and ceritinib is the ALK G1202R solvent front mutation. The detection of resistance mutations has been improved with the evolution of biotechnology, making it possible to search for tumor-derived plasma free DNA as a liquid biopsy in cases where tissue biopsies are difficult to obtain. Digital PCR (dPCR) is an improved method of the conventional PCR method, which is more accurate and allows absolute quantification than the RT-PCR method. Materials and Methods: For a total of 9 patients, 2 patients newly diagnosed with ALK+ NSCLC by tissue biopsy and about to receive ALK-TKI and 7 patients already diagnosed with ALK+ NSCLC and receiving ALK-TKI, 10 ml of plasma was collected in addition to the blood collection at each 3-monthly visit. cfDNA was extracted and digital PCR was used to simultaneously detect 10 ALK mutations (T1151ins, C1156Y, L1196M, G1269A, F1174L, L1152R, V1180L, I1171T, G1202R, S1206Y). This Study was supported by an Investigator Initiated Research (IIR) from Pfizer. Results: The total number of samples analyzed in 9 cases was 65, and the median number of samples collected in each case was 7 (minimum 2 - maximum 12). cfDNA concentration was a median of 9.9 ng/ml of plasma (4.0-35.8 ng/ml). The number of samples detected for each mutation was 32 for G1202R, 16 for C1156Y, 5 for G1269A, 4 for F1174L, 1 for T1151ins, and 1 for I1171T. G1202R was detected in 19 of 37 samples during treatment with alectinib. The median time from detection of G1202R to clinical disease progression was 388 days (123-2004 days), with repeated emergence and disappearance in some cases. Conclusions: The dPCR method was highly sensitive in detecting gene mutations with low allele frequency. It was also found to be able to monitor variable resistance mutations over time during ALK-TKI treatment. In addition, we found that the appearance of G1202R did not always indicate clinical acquisition of resistance that required drug modification. A limitation of this study is that the mutations detected are not distinguishable between the same allele or Cis/trans. In particular, EML4-ALK forms a trimeric protein, suggesting that single mutations such as G1202R and drug susceptibility do not always match in clinical specimens.

Citation Format: Takaaki Sasaki, Noriko Hirai, Yoshinori Minami, Shunsuke Okumura, Shin-ichi Chiba, Ryohei Yoshida. Longitudinal minimally invasive monitoring of resistance mutations in ALK rearranged lung cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 503.