Metastatic lung squamous cell carcinoma: no recurrence after chemoimmunotherapy and pembrolizumab maintenance

What happened, in summary

This 65-year-old man, a current smoker with no prior medical history, was found to have an abnormal chest X-ray during a regular checkup. He had no symptoms and had an ECOG performance status of 0. Chest CT showed a mass in the right middle lobe, enlarged mediastinal lymph nodes, and small nodules in both lungs. PET/CT showed increased uptake in the right middle lobe and mediastinal lymph nodes, while brain MRI showed no brain metastasis. Physical examination was normal, and he remained asymptomatic at diagnosis. Bronchoscopy of the lung lesion showed p40-positive, TTF-1-negative lung squamous cell carcinoma. The staining pattern supported squamous differentiation rather than adenocarcinoma. The cancer was staged cT3N2M1c, Stage IVB, with mediastinal nodal involvement and bilateral lung nodules. Molecular testing found an EGFR exon 19 deletion, and PD-L1 expression was very high, with TPS 95%. Although EGFR-TKI therapy is commonly used first for EGFR-mutated NSCLC, this patient chose chemotherapy plus immunotherapy. He began carboplatin, nab-paclitaxel, and pembrolizumab. After 4 cycles, CT showed that both the main lung tumor and metastatic lesions had shrunk, and he had no adverse events. He then continued with pembrolizumab alone. The primary tumor and metastatic lesions kept shrinking during pembrolizumab monotherapy, and a good response was maintained for 2 years without reported adverse events. After completing the scheduled 2-year pembrolizumab course, he moved to regular hospital visits with blood tests and imaging. As of April 2025, PET/CT 3 years after treatment began showed no sign of recurrence on follow-up imaging.