Comparison of 4DST and FDG PET/CT imaging for advanced clear cell renal cell carcinoma

1430 Objectives 4’-[methyl-11C]-thiothymidine (4DST) has been developed as an in vivo cell proliferation marker based on its DNA incorporation mechanism. We evaluated the potential of 4DST for imaging cellular proliferation in advanced clear renal cell carcinoma (cRCC), compared with FDG. 4DST and FDG uptake was compared with biological findings based on surgical pathology. Methods Twenty areas of cRCC in 5 patients (mean age, 65 ± 11 yrs) were examined by 4DST and FDG PET/CT. The SUVmax of cRCC on both 4DST and FDG were compared with 1) the Ki-67 index of cellular proliferation 2) Fuhrman classification system for nuclear grade (G) in RCC and 3) pathological grade of mammalian target of rapamycin (mTOR) as a central regulator of cell metabolism, growth and proliferation. Results All cases had a single renal cell tumor (mean 9.3 ± 3.2 cm, range 5.5-13.0cm) showing clear uptake of FDG (mean SUVmax: 4.5) and 4DST (mean SUVmax: 8.3). The correlation coefficient between SUVmax and Ki-67 index was higher with 4DST (r = 0.61) than FDG (r =0.43). Tumor 4DST (G0: 1.4, G2: 2.6, G2 5.6, G4; 5.7) and FDG uptake (G0: 1.8, G2: 2.9, G2 3.7, G4; 4.1) was related to Fuhrman classification system. 4DST uptake was increased with mTOR grade (G0: 3.1, G1: 4.8, G2: 4.7, G3: 6.2), in contrast FDG was unrelated to mTOR grade (G0: 2.8, G2: 4.0, G2 3.3, G4: 3.6). Conclusions A higher correlation with proliferation of cRCC was confirmed for 4DST than for FDG. 4DST and FDG had relation with nuclear grade. 4DST has potential for evaluation of therapeutic effect with mTOR inhibitor in patient with cRCC. Research Support a Grant-in Aid for Young Scientists (B) No. 24791362 from the Japan Society for the Promotion of Science