Complete remission after pembrolizumab monotherapy in a non-small cell lung cancer patient with PD-L1 negative, high tumor mutational burden, and positive tumor-infiltrating lymphocytes: A case report.

Rationale: Immune checkpoint inhibitors have been used to treat cancer patients. Non-small cell lung cancer (NSCLC) patients with a high expression level of programmed cell death ligand-1 (PD-L1) could benefit from immune checkpoint inhibitor monotherapy. However, treating NSCLC patients with PD-L1 negative is still a clinical challenge. The utilization of new-type tumor markers as predictive indicators of therapeutic efficacy, with the aim of guiding clinical medication strategies, has emerged as a paramount focus of clinical investigation and interest.

Patient Concerns And Diagnoses: We reported a 72-year-old male with cough diagnosed as poorly differentiated metastatic lung adenocarcinoma (cT3N2M1, stage IV). He tested negative for driver gene mutations, and PD-L1 negative (＜1%), but a high tumor mutational burden (30.9 and 39.1 mutations/Mb in the lung tissue and blood, respectively), and positive tumor-infiltrating lymphocytes.

Interventions: The patient received pembrolizumab monotherapy.

Outcomes: After 8 treatment cycles over 5 months, repeat examinations showed significantly reduced lung mass and circulating tumor DNA abundance. The patient reached clinical complete remission and had long-term survival with no significant adverse events.

Lessons: A comprehensive evaluation of multiple tumor biomarkers should be considered in NSCLC patients. Pembrolizumab monotherapy could benefit NSCLC patients with negative driver genes, PD-L1 negative, a high tumor mutational burden, and positive tumor-infiltrating lymphocytes.