18F-Deoxyglucose (18F-FDG) Positron Emission Tomography/Computed Tomography (PET/CT) Monitoring of Dynamic Growth Characteristics of Walker-256 Tumor Models in 3 Different Locations in Rats.

BACKGROUND We explored the ideal method of establishing subcutaneous, breast, and liver tumor models using the same Walker-256 cells, and investigated the dynamic growth characteristics using ¹⁸F-deoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT), which provides basic information for choosing an experimental animal model. MATERIAL AND METHODS We established tumor models in 3 locations (subcutaneous, breast, and liver) in W256 Sprague-Dawley rats. ¹⁸F-FDG PET/CT imaging was performed from 6 days to 18 days after injecting the cells subcutaneously. Tumor volume of interest (VOI), maximum standard uptake value (SUVmax), and average standard uptake value (SUVavg) were obtained from the image. The difference of the growth characteristics in tumor volume and SUVs among the 3 groups were compared. Histopathology of the tumors was also analyzed. RESULTS The tumors in subcutaneous location grew fastest, followed by tumors located in the breast, and tumors in the liver grew slowest. Significant differences in tumor VOI (p=0.01) were observed. ¹⁸F-FDG uptake of the subcutaneous and breast tumors increased until day 10 and then decreased subsequently. ¹⁸F-FDG uptake of the liver tumor reached a peak at day 10, and necrosis peaked at day 12. The histopathology analysis results indicated that the necrosis was mainly located in the center of tumors while the viable tissues were located on the periphery. Similarly, CD 31 and Ki-67 were mainly expressed on the tumor periphery. CONCLUSIONS Subcutaneous, breast, and liver tumor models were easy to establish using Walker-256 cells. They showed fast growth and high uptake of ¹⁸F-FDG. These kinds of tumor models were optimal in evaluating anti-tumor efficacy by ¹⁸F-FDG PET/CT, but it may be essential to determine the best time-points at which to use it.