A new rat model of bone cancer pain produced by rat breast cancer cells implantation of the shaft of femur at the third trochanter level.

Bone cancer pain remains one of the most challenging cancer pains to fully control. In order to clarify bone cancer pain mechanisms and examine treatments, animal models mimicking the human condition are required. In our model of Walker 256 tumor cells implantation of the shaft of femur at the third trochanter level, the anatomical structure is relatively simple and the drilled hole is vertical and in the cortical bone only 1-2 mm in depth without injury of the distal femur. Pain behaviors and tumor growth were observed for 21 days. And neurochemical changes were further investigated in this model. The results showed that cancer-bearing rats demonstrated a decreased limb use score from day 14, an increased spontaneous flinching and guarding times from day 7 and a decreased withdrawal threshold from day 6. The tumor infiltration of bone was monitored by MRI and further verified by histological examination. C-fos and the capsaicin receptor (TRPV1) positive neurons were more expressed in cancer-bearing rats and the substance P expression has no difference, suggesting that neurons were activated in the model. Our animal model demonstrated time-dependent tumor growth and pain behaviors and will be a novel animal model of bone cancer pain in the future.