Durable complete response after a single cycle of pembrolizumab-based chemoimmunotherapy in metastatic squamous cell lung cancer: a case report

Abstract

Squamous cell lung cancer (SqCLC) is an aggressive subtype of non-small cell lung cancer (NSCLC), frequently associated with distant metastases. Although immune checkpoint inhibitors improve survival, complete responses after a single cycle of pembrolizumab-based chemoimmunotherapy are exceedingly rare. A 77-year-old Turkish male with hypertension and type 2 diabetes presented with acute left arm weakness. He was a never-smoker with a history of urothelial carcinoma. Brain MRI revealed right paracentral and cerebellar metastatic lesions, while thoracic imaging showed multiple pulmonary nodules. Histopathology confirmed metastatic SqCLC with a PD-L1 tumor proportion score of 40%. The patient underwent craniotomy and stereotactic radiosurgery, followed by one cycle of gemcitabine, carboplatin, and pembrolizumab. Treatment-related toxicities (grade 2 fatigue, neutropenia, mild infection, and grade 1 skin toxicity) resolved with supportive care. Despite clinical stability, the patient declined further therapy. Follow-up imaging demonstrated complete resolution of all lesions. At 24 months, he remains in complete remission. This case illustrates a rare, durable complete response—including intracranial disease—after a single cycle of pembrolizumab-based chemoimmunotherapy in metastatic SqCLC.