Figure 4.

Representative images with various response patterns by ¹⁸F-FLT PET. (A) A 65-year-old woman with stage IIIA lung adenocarcinoma who achieved a partial response (PR) and 27.8 months of PFS after pembrolizumab therapy. The sum of ¹⁸F-FLT uptake (TLP) of the lesions at baseline decreased by 46.1% at 2 weeks after therapy, while the sum of the diameter was not changed (−0.1%). (B) A 76-year-old man with stage IIIC lung squamous cell carcinoma who achieved PR after proliferative pseudoprogression and 6.4 months of PFS after pembrolizumab therapy. ¹⁸F-FLT uptake of the primary lesion in the left lower lobe at baseline increased by 58.4% at 2 weeks after therapy followed by a decrease of ¹⁸F-FLT uptake (−31.4%) in 6-week PET images. (C) A 77-year-old man with stage IVA non-small cell lung cancer, not otherwise specified, who experienced PR followed by early acquired resistance and short PFS (5.2 months). TLP of the primary lesion in the left upper lobe at baseline dramatically decreased by 94.4% at 2 weeks after pembrolizumab therapy. However, the TLP at 2 weeks increased by 37.3% at 6 weeks after therapy. (D) A 71-year-old man with stage IVb lung adenocarcinoma who showed a dissociated response and experienced progressive disease and short PFS (3.3 months). TLP of the primary lesion of right S6 decreased by 100% at 2 weeks after therapy, while that of right hilar lymph node increased by 86.1%. ¹⁸F-FLT, 3′-deoxy-3′-[¹⁸F]-fluorothymidine; PET, positron emission tomography; PFS, progression-free survival; TLP, total lesion proliferation.