Fig. 2.

A case of pseudoprogression in a 52-year-old man with NSLCL, who was receiving immune checkpoint inhibitor therapy. Axial CT and ¹⁸F‑FDG-PET/CT imaging obtained before the start of treatment show a metabolically active tumor in the right lower lobe and an ipsilateral hilar lymph node metastasis. Four weeks after treatment initiation, the tumor slightly decreased in size and showed reduced ¹⁸F‑FDG uptake. However, we observed a newly developed, metabolically active metastasis in the 4th thoracic vertebral body measuring <1.0 cm. Treatment was continued and PET-CT performed 10 weeks after the start of treatment showed no increased ¹⁸F‑FDG uptake in the 4th thoracic vertebral body. The ¹⁸F‑FDG uptake in the primary tumour in the right lower lobe further decreased. The newly developed, metabolically active, ground-glass opacities were radiation-associated. Thirty-one weeks after the start of treatment, ¹⁸F‑FDG PET-CT evidenced disease progression in both the primary tumour and the metastasis in the 4th thoracic vertebral body. Upper row: CT in lung window, middle row: axial fused PET/CT image lower row: axial fused PET/CT image