Pathological Complete Response to a Single Dose of Pembrolizumab-Based Chemoimmunotherapy for Squamous Cell Carcinoma of the Lung: A Case Report

We herein describe a patient with non-small-cell lung cancer who achieved pCR with a single dose of pembrolizumab-based chemoimmunotherapy followed by surgery. A 61-year-old man was referred to our hospital with wheezing and an abnormal chest shadow. Squamous cell carcinoma of the left lower lobe, cT2aN1M0 stage IIB, was diagnosed and pembrolizumab-based chemoimmunotherapy was initiated at the patient's request. One month later, chest CT revealed new ground-glass opacities of the lungs, which were judged to be a CTCAE grade 2 pneumonitis due to an immune-related adverse event (irAE). Therefore, steroid therapy was initiated. Prednisolone was tapered and discontinued as symptoms improved. A sleeve resection of the left lower lobe was performed, and a pathological complete response (pCR) was confirmed in a resected specimen. There has been no recurrence for 1 year and 7 months without treatment. This is the first case report of pCR to a single dose of chemoimmunotherapy followed by surgery for lung cancer. The present results suggest the potential of a single dose of chemoimmunotherapy to achieve pCR and cause irAEs in some patients.