ACTN4 Gene Amplification and Actinin-4 Protein Expression for Osimertinib Efficacy in EGFR-Mutant NSCLC.

Actinin-4 (gene name: ACTN4) is an actin-bundling protein implicated in cancer invasion and metastasis. This study evaluated whether ACTN4 amplification and actinin-4 protein expression were associated with osimertinib efficacy in epidermal growth factor receptor-mutant non-small cell lung cancer. We retrospectively analyzed 63 patients with epidermal growth factor receptor-mutant non-small cell lung cancer treated with osimertinib as first-line treatment. Immunohistochemistry was performed for pretreatment tumor tissues. Actinin-4 immunohistochemistry positivity was defined as positive staining of ≥ 30% tumor cells. In positive cases, ACTN4 amplification was assessed via fluorescence in situ hybridization. Progression-free survival and overall survival were compared across groups. Among 63 patients (median age: 73 years, 52 with Eastern Cooperative Oncology Group performance status 0-1, 63 with adenocarcinoma; epidermal growth factor receptor mutations: 19del/L858R/uncommon = 32/24/7), there were 33 and 30 actinin-4 immunohistochemistry-positive and actinin-4 immunohistochemistry-negative cases, respectively. The propensity score-weighted overall survival and progression-free survival were significantly shorter for actinin-4 immunohistochemistry-positive patients than for actinin-4 immunohistochemistry-negative patients (overall survival: hazard ratio, 2.76; 95% confidence interval, 1.02-7.45; progression-free survival: hazard ratio, 1.91; 95% confidence interval, 1.03-3.54). Among the 33 actinin-4 immunohistochemistry-positive cases, four showed positivity in ACTN4 fluorescence in situ hybridization. Overall survival and progression-free survival were numerically shorter for patients with ACTN4 positivity than for those with ACTN4 negativity in fluorescence in situ hybridization. The findings suggest that ACTN4 amplification and actinin-4 protein expression are prognostic markers for poor osimertinib efficacy in epidermal growth factor receptor-mutant non-small cell lung cancer.