Positron emission tomography with [¹⁸F]-3′-Deoxy- 3′fluorothymidine (FLT) as a predictor of outcome in patients with locally advanced resectable rectal cancer: A pilot study

Purpose: This pilot study was performed to evaluate whether tumor uptake of ¹⁸F-labeled 3′-deoxy-3′fluorothymidine (FLT), a proliferative radiotracer, at baseline and early during therapy, is predictive of outcome in locally advanced rectal cancer. Procedures: Fourteen patients underwent positron emission tomography (PET) with 2-deoxy-2-[ ¹⁸F]fluoro-d-glucose (FDG) and FLT before therapy and PET with FLT approximately 2 weeks after initiating neoadjuvant chemoradiotherapy. FLT and FDG uptake were evaluated qualitatively and by maximum standardized uptake value (SUV_max). Tumor FLT and FDG uptake were correlated with disease-free survival (DFS). Results: Thirteen patients underwent surgery after therapy, one died before surgery with progressive disease. FDG-PET/computed tomography detected regional lymph node metastases in five and FLT-PET was positive in one. High pretherapy FDG uptake (SUV_max ≥ 14.3), low during-therapy FLT uptake (SUV_max < 2.2), and high percentage change in FLT uptake (≥60 %) were predictive of improved DFS (p < 0.05 for all three values). Conclusion: Pretherapy FDG uptake, during-therapy FLT uptake, and percentage change in FLT uptake were equally predictive of DFS.