EP1.04-11 Frequency of Microsatellite Instability (MSI) in Brazilian TKI Non-Treatable Non-Small Cell Lung Cancer (NSCLC) Patients

Abstract

Lung cancer is the most common cause of cancer deaths worldwide. Personalized medicine based on driver mutations has improved tailored treatment for patients with non-small cell lung cancer (NSCLC). However, only a subset of patients is benefited with tyrosine kinase inhibitors. Non-treatable advanced NSCLC patients may be eligible for treatment with immunotherapies. Recently, microsatellite instability (MSI) phenotype was reported as a predictive biomarker of response to immunotherapy, making it a crucial biomarker for clinical management for NSCLC patients. This study aimed to determine MSI frequencies in Brazilian NSCLC patients who are not eligible for TKi therapy. 522 patients diagnosed with NSCLC patients at Barretos Cancer Hospital (Brazil) were evaluated. All samples were molecularly analyzed for EGFR (exons 18, 19, 20 and 21), KRAS (codons 12/13) and BRAF (exon 11 and 15) mutations by PCR followed by Sanger direct sequencing. The molecular MSI evaluation was performed using a hexa-plex marker panel by PCR followed by fragment analysis. The mean age of the patients was 61y (22-87) and 54% were male. EGFR, KRAS, and BRAF wild-type status were identified in 62.6% (327/522) of cases. In 297 EGFR/KRAS/BRAF wild-type cases, MSI analysis was performed and we observed the presence of MSI-H in only three (1%) cases. Overall, two out of these three patients were female and one was male, the age at the diagnosis ranged from 55 to 76 years old, they were current or former smokers and all three cases were diagnosed at stage IV. Of note, one of the patients with MSI-high status received treatment with immune checkpoint inhibitor, and he is the only one out of the three patients that remains alive with 51-months survival. The frequency of MSI-high status is low in Brazilian NSCLC patients, in accordance with other population literature. Nevertheless, these MSI-positive patients are eligible for immunotherapy approaches.