Abstract Spontaneous regression (SR) of lung cancer is exceptionally rare, with only sporadic cases documented in the literature. Proposed mechanisms include immune-mediated responses triggered by infection, paraneoplastic syndromes, or tissue trauma following diagnostic procedures. We report the case of a 60-year-old male, current smoker with a 50–pack-year history, who presented with hemoptysis and was found to have a 1.9 cm mass in the right upper lobe. PET/CT showed a moderately hypermetabolic lesion without metastases. Endobronchial ultrasound (EBUS)-guided needle aspiration demonstrated a poorly differentiated adenocarcinoma with a high PD-L1 expression (>75%). Three weeks after EBUS, a preoperative chest CT revealed a marked reduction in tumor size to 0.8 cm. The patient proceeded to surgical resection; however, pathological examination of the resected lobe demonstrated no residual malignancy, only fibrotic tissue with chronic inflammation. This case represents a rare instance of histologically verified lung cancer undergoing spontaneous regression. The temporal association with diagnostic biopsy and the presence of high PD-L1 expression may be consistent with an immune-mediated process.
Näslund et al. (Fri,) studied this question.