Conversion therapy with chemoimmunotherapy induced pCR in a stage IV lung squamous cell carcinoma patient harboring <i>EGFR</i> exon 20 insertion

This case study details an innovative conversion therapy strategy in a 58-year-old Asian male with baseline stage cT₄N₁M_1b advanced lung squamous cell carcinoma (SCC) harboring a rare <i>EGFR</i> exon 20 insertion mutation with concurrent high PD-L1 expression who achieved a pathologic complete response (pCR) after preoperative immunotherapy plus chemotherapy. The patient initially presented with coughing and bloody sputum and was comprehensively diagnosed via PET/CT scanning, bronchoscopic biopsy and next-generation sequencing. After four cycles of platinum‒paclitaxel chemotherapy plus immunotherapy with pembrolizumab (a PD-1 blockade), significant primary tumor shrinkage and the disappearance of oligometastasis in the right adrenal gland were discovered via CT scans. The subsequent salvage lung surgery resulted in a pCR, and the patient continued postoperative maintenance immunotherapy. No evidence of disease relapse or immune-related adverse events occurred after a post-surgery follow-up time of 9.4 months. This case highlights the potential value and challenges of immunotherapy plus chemotherapy as conversion therapy strategy in treating patients with non-small cell lung cancer (NSCLC) harboring rare <i>EGFR</i> exon 20 insertions.