B80-5-53 Advanced Squamous Cell Lung Carcinoma Harboring Epidermal Growth Factor Receptor Mutation: A Rare Clinical Case

Abstract Background Non-small cell lung cancer accounts for approximately 85% of lung cancers, with an estimated 1 million new lung cancer cases in the Southeast Asian and Western Pacific regions combined. The use of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKI) ushered in a new era in treatment of lung cancer, greatly improving the outcomes of EGFR mutation-positive adenocarcinomas. The efficacy and benefit of EGFR TKIs have been established beyond doubt in EGFR mutation-positive ADCs; however, its efficacy has not been well studied in EGFR mutation-positive lung squamous cell carcinomas and continues to be an area of active research. We herein present a case of an EGFR mutated squamous cell lung cancer that responded to a third-generation EGFR TKI, Osimertinib in combination with systemic chemotherapy. Case This is a case of a 48-year-old Filipino man who presented with non-productive coughing which, over the past 3 weeks, would aggravate to exertional when molecular profiling results confirmed the presence of the Exon 19 mutation, third generation TKI, Osimertinib, was started. As of this writing, the patient is already on his 3rd month of taking Osimertinib and has already completed 5 cycles of chemotherapy. Re-evaluation PET-CT Scan showed a partial response on the primary lung tumor (51% decrease in the size by RECIST), associated with regression of the involved mediastinal lymph nodes and the T10 osseous metastasis. Discussion Squamous cell carcinoma (SCC) accounts for approximately 20% of all lung cancers. EGFR-mutant SCC is an uncommon molecular subtype, representing an estimated 3-18% of cases. This molecular finding has important therapeutic implications, as EGFR-targeted tyrosine kinase inhibitors, typically reserved for adenocarcinoma, may provide clinical benefit in select patients. This case highlights the diagnostic and therapeutic challenges of EGFR-mutated SCC. It reinforces the value of molecular testing in advanced SCC to guide precision-based management and optimize patient outcomes. This abstract is funded by: None