Radiofrequency ablation of experimental bone metastases in nude rats

Animal models are indispensable to investigate bone metastasis and to test different preclinical therapy options. Radiofrequency ablation is an upcoming technique for palliating pain from bone metastases. The aim of this study was to generate osteolytic lesions and to enable a technique to achieve access to the bone to successfully carry out radiofrequency ablation.

Human breast cancer cell line MDA-MB-231 (10(5) tumor cells) was implanted into the femur of 10 nude rats using a drill hole after arthrotomy of the knee joint and opening of the femur through the notch. Weekly CT- and MRI-scans were performed to document number and size of bone metastases. Radiofrequency ablation (22G bipolar and impedance-controlled RF-applicator, 2-4 Watt, 3 min application time) was carried out. One week after RFA, the animals were sacrificed and macroscopic and histological examination followed. For statistical analysis, paired comparison procedures were used.

Inoculation of the tumor cells was well tolerated. The mean time of the surgical procedure was 6 minutes. All animals developped local bone metastases. Mean time to metastasis was 8 weeks (range 7-10 weeks) after tumor cell implantation. No leakage of tumor cells and no soft part metastases occurred. Radiofrequency ablation was performed without complications. Imaging showed a complete ablation of the bone tumor in all rats. Histological findings confirmed a circular necrosis with an extensive destruction of tumor cells leaving a necrosis cavity.

The experimental model presented here describes the first time the ability to carry out radiofrequency ablation in nude rats with intrafemoral induced osteolytic metastases of human breast cancer. RFA in human breast cancer cell line in nude rats is a feasible and useful possibility to evaluate and to test different RF-procedures. Additional treatment options like local chemotherapy or chemoembolization can be performed.