OPTIMIZATION OF MOLECULAR GENETIC DIAGNOSTICS OF PATIENTS WITH ADVANCED NON-SMALL CELL LUNG CANCER BY INTRODUCING ROS1 TESTING IN THE REPUBLIC OF KAZAKHSTAN

Relevance: Currently, molecular diagnosis in NSCLC in Kazakhstan includes detection of EGFR, ALK driver mutations status, and PD-L1-status, but not ROS1, what limits the access of patients with this driver mutation to vital therapy. The study aimed to optimize the methods of molecular genetic diagnosis of patients with NSCLC by introducing ROS1 testing in the Republic of Kazakhstan. Methods: The biopsy and surgical material of non-small cell lung cancer (NSCLC) fixed in 10% buffered formalin was studied. After the initial morphological diagnosis of adenocarcinoma, EGFR, and ALK mutation status determination, EGFR, and ALK-negative tumor assays were sent for further determination of ROS1 mutation status. First, we performed immunohistochemistry (IHC) using the Ventana BenchMark Ultra platform using the ROS1 antibody (SP283) and the OptiView DAB Detection Kit imaging system. After that, samples with positive and doubtful IHC results were sent for RT-PCR (reverse transcriptase polymerase chain reaction) to confirm the ROS1 mutation status. Results: A total of 99 tumor samples from patients with EGFR-negative and ALK-negative lung adenocarcinoma were studied by IHC from January 01 till September 30, 2022. The results of IHC staining were assessed as: 0 (negative) – 59 samples, 1+ (negative) – 25 samples, 2+ (doubtful) – 12 samples, 3+ (positive) – 3 samples. Cases with ≥70% immunostaining were considered positive. Samples with an IHC stain score of 2+ (doubtful), 3+ (positive), and a few samples of 1+ were sent for confirmation by PCR. Overall, 22 samples were tested using RT-PCR, and results were considered as follows:1 (4%) – positive, 13 (59%) – negative, 8 (37%) -– invalid. Conclusion: A large proportion of positive and questionable results were obtained when determining ROS1 mutation status using IHC, and a large proportion of invalid results during subsequent RT-PCR testing. Choosing methods for nationwide ROS1 implementation, one should evaluate the economics of the methods to be implemented and compare them with a standard validated FISH method.