Emergence of lung cancer with a low PD-L1 expression level after the administration of immune check point inhibitor for lung adenocarcinoma with a high PD-L1 expression level: A case report.

backgroundCheckpoint therapy against PD-1 has proven effective and positive results have been observed in several types of cancer, including lung cancer, renal cancer, lymphoma and melanoma. However, the effects of long-term ICI treatment remain insufficient and the development of resistance is an issue that remains to be solved. CASE PRESENTATION: A 70-year-old man was diagnosed with lung adenocarcinoma (stage IVB, T4N3M1c) with a high programmed death ligand-1 (PDL1) expression level (tumor proportion score [TPS]: 80% score at the time of the diagnosis, before treatment). At 16.5 months after the start of pembrolizumab, following the administration of 22 cycles of pembrolizumab, a new lesion appeared. Biopsy by video-assisted thoracic surgery (VATS) was performed for this lesion and a pathological diagnosis of lung adenocarcinoma with a low PD-L1 expression level. After the operation, pembrolizumab treatment was continued. The patient currently remains alive without disease progression at 20 months after the initial therapy.

conclusionsOur case highlights the importance of biopsy by VATS during immune checkpoint inhibitor (ICI) treatment when deciding the treatment strategy for newly confirmed tumors.