Abstract
PURPOSE: Fluorescence in situ hybridization (FISH) using tumor tissue is the gold standard for detection of anaplastic lymphoma kinase (ALK) rearrangement in non-small cell lung cancer (NSCLC). However, this method often is not repeatable due to difficulties in the acquisition of tumor tissues. Blood-based liquid biopsy using reverse transcription polymerase chain reaction (RT-PCR) is expected to be useful to overcome this limitation. Here, we investigated the feasibility of liquid biopsy using plasma and platelets for detection of ALK rearrangement and prediction of ALK inhibitor treatment outcomes. METHODS: ALK-FISH assays were performed in 1128 tumor specimens of NSCLC between January 2015 and June 2018. We retrospectively analyzed formalin-fixed paraffin-embedded (FFPE) tissues from previously confirmed FISH-positive (n = 199) and -negative (n = 920) cases. We recruited patients who had available tissue specimens and agreed to venous sampling. RNA was extracted from FFPE blocks, plasma, and platelets. Fusion RNA of echinoderm microtubule-associated protein-like 4 (EML4)-ALK was detected by quantitative PCR. RESULTS: Thirty-three FISH-positive and 28 FISH-negative patients were enrolled. In validation, data compared with FISH, RT-PCR using FFPE tissues showed 54.5% sensitivity, 78.6% specificity, and 75.5% accuracy. Liquid biopsy had higher sensitivity (78.8%), specificity (89.3%) and accuracy (83.6%). Higher positivity for liquid biopsy was shown in subgroups with delayed (≥ 6 months from diagnosis) blood sampling (plasma, 85.7%; platelets, 87.0%). In 26 patients treated with crizotinib, the platelet-positive subgroup showed longer median duration of treatment (7.2 versus 1.5 months), longer median progression-free survival (5.7 months versus 1.7 months), a higher overall response rate (70.6% versus 11.1%), and a higher disease control rate (88.2% versus 44.4%) than the platelet-negative subgroup. CONCLUSION: Liquid biopsy could have applications in the diagnosis of ALK-positive NSCLC, even when using RT-PCR, and platelets can be useful for predicting treatment outcomes of ALK inhibitors.