What happened, in summary

A 33-year-old woman who had never smoked sought care in July 2019 for persistent cough and blood-streaked sputum. CT showed a 4.9 cm mass in the left lower lung, and brain imaging showed a right parietal lesion considered suspicious for metastasis. Lung biopsy confirmed primary pulmonary lymphoepithelioma-like carcinoma, with EBER positivity and no detected EGFR, ROS1, RAS/RAF, or PIK3CA alteration. The cancer was classified as Stage IV. She received 7 cycles of nab-paclitaxel with toripalimab and then continued toripalimab maintenance, initially achieving stable disease. When the lung lesion enlarged slightly in 2021, she received radiation. Later imaging showed marked enlargement that looked concerning for progression, but repeat biopsy found chronic inflammation. She underwent left lower lobectomy in January 2022, and pathology showed no residual cancer. A treated brain lesion also enlarged and caused headaches, numbness, and seizures. After radiation and later craniotomy, the brain pathology showed necrosis and inflammation without definitive tumor. Another lung lesion in 2023 also proved inflammatory and improved with antiviral treatment. Through May 2025, follow-up showed no clear recurrence or metastasis, with progression-free survival longer than 70 months. Repeated pathology showing inflammation or treatment effect, together with long-term follow-up, supported pseudoprogression rather than active cancer.