Determination of ROS1 positivity by immunohistochemistry in a multicentric cohort of 426 non-small-cell lung cancer cases in India

Abstract

Introduction: ROS1 is a receptor tyrosine kinase of the insulin receptor family that acts as a driver oncogene in 1%–2% of non-small cell lung carcinoma (NSCLC) patients via a gene translocation between ROS1 and other genes, the most common one being CD74. Histologic and clinical features that are associated with ROS1 translocations include never smokers, younger age, and adenocarcinoma (AC) histology. The identification of ROS1 fusion is important because it responds to targeted therapies such as crizotinib that can greatly improve the survival of the patient. The goal of this study was to determine the percentage of population harboring ROS1 mutation in India. Materials and Methods: ROS immunohistochemistry (IHC) method was optimized using Cell Signalling Technology, ROS antibody (ROS1 clone D4D6 rabbit mAb), and appropriate positive and negative controls in a fully automated procedure using Ventana automated stainer. Approximately 2000 retrospective lung cancer cases from six different Apollo hospitals were identified. The formalin-fixed paraffin-embedded blocks and corresponding diagnostic and demographic data were retrieved. A total of 426 cases with confirmed diagnosis of NSCLC were then tested by IHC for ROS1. Results: Given the retrospective nature of the cancer cases and diagnostic data being used for the study, there was high attrition in the availability of the blocks and data. Among the 2000 cases examined, there were 604 cases that were initially reported as lung cancer in the hospital medical records and for whom corresponding blocks were available, but blocks for only 485 cases had sufficient tumor content, as judged by hematoxylin and eosin staining and microscopic examination, to enable testing for ROS1 staining. Of these 485 cases, 225 were confirmed AC cases. A single case stained positive for ROS1 among the 225 AC cases. The percentage is calculated to be 0.44% based on this single positive case. No positive case was observed in squamous cell carcinomas or other cancers of the lung such as neuroendocrine tumors, germ cell tumors, and adenoid cystic tumors. Conclusion: The percentage positivity for ROS1 in the study comprising 225 Indian NSCLC AC cases appeared similar to the 0.3%–1.6% range reported for smokers and lower than 0.9%–1.7% positivity reported in mixed patient populations.