Journal Article

Revisiting ALK (D5F3) immunohistochemistry: Insights into focal staining and neuroendocrine differentiation

Kim, Meejeong, Sung, Yeoun Eun

2024

Overview

Background Screening for anaplastic lymphoma kinase (ALK) rearranged non‐small cell lung cancer (NSCLC) is crucial for identifying patients eligible for targeted therapy. The FDA‐approved ALK (D5F3) immunohistochemistry (IHC) assay, used with the OptiView Amplification Kit, demonstrates excellent sensitivity and specificity in detecting these patients. However, the clinical significance of resulting focal positivity remains unclear, and ALK (D5F3) expression unrelated to ALK fusion is observed in some cases of neuroendocrine differentiation. This study aims to validate these findings with molecular testing and contribute to the accurate interpretation of ALK (D5F3) IHC results. Methods A total of 1619 patients diagnosed with NSCLC and neuroendocrine carcinoma were evaluated using ALK (D5F3) IHC. For cases with strong but focal expression and those with diffuse strong positivity in neuroendocrine differentiation, ALK fluorescence in situ hybridization (FISH) and/or next‐generation sequencing (NGS) tests were performed. Results Seven out of 1109 adenocarcinomas (0.6%) and six out of 289 squamous cell carcinomas (2.1%) exhibited strong focal ALK (D5F3) expression. Nine out of 209 neuroendocrine carcinomas (4.3%) showed homogeneously strong ALK (D5F3) expression. All these cases, including adenocarcinoma with neuroendocrine differentiation and combined small cell carcinoma, were negative for ALK fusions by FISH and/or NGS. Conclusion This study demonstrates that strong but focal ALK (D5F3) immunostaining and strong expression in neuroendocrine differentiation may not indicate ALK fusion. By considering these findings, we can improve the accuracy of patient selection for targeted therapy by minimizing false‐positive interpretations of ALK (D5F3) staining. We investigated the clinical significance of focal strong ALK (D5F3) immunostaining in NSCLC and neuroendocrine differentiation cases. Our findings revealed that these staining patterns can occur independently of ALK fusion, suggesting the need for revised interpretation guidelines to avoid false‐positive results and improve patient selection for targeted therapy.

• Publisher: John Wiley & Sons Australia, Ltd,John Wiley & Sons, Inc,Wiley
• Subject: Adult / Aged / Aged, 80 and over / Algorithms / anaplastic lymphoma kinase / Anaplastic Lymphoma Kinase - genetics / Anaplastic Lymphoma Kinase - metabolism / Biomarkers, Tumor - genetics / Biomarkers, Tumor - metabolism / Biopsy / Carcinoma, Neuroendocrine - genetics / Carcinoma, Neuroendocrine - metabolism / Carcinoma, Neuroendocrine - pathology / Carcinoma, Non-Small-Cell Lung - genetics / Carcinoma, Non-Small-Cell Lung - metabolism / Carcinoma, Non-Small-Cell Lung - pathology / Cell Differentiation / Demographics / false‐positive reactions / FDA approval / Female / Genes / Humans / Immunohistochemistry / Immunohistochemistry - methods / In Situ Hybridization, Fluorescence - methods / Kinases / Lung cancer / Lung Neoplasms - genetics / Lung Neoplasms - metabolism / Lung Neoplasms - pathology / Male / Middle Aged / Mutation / neuroendocrine tumors / non‐small cell lung cancer / Original / Patients / Sample size / Squamous cell carcinoma / staining