Radiofrequency ablation of solid tumors is produced by frictional heating caused when ions in the tissue attempt to follow the changing directions of a high-frequency alternating current. The radiofrequency probe is typically placed under ultrasound guidance, and the ablation is performed with real-time ultrasound monitoring. Radiofrequency ablation has been demonstrated to be effective in the treatment of unresectable hepatic tumors, and promising results have also been obtained in tumors of the lung, bone, brain, kidney, prostate gland, and pancreas. Most recently, radiofrequency ablation has been tested in the treatment of invasive breast tumors. A preliminary study reported that intraoperative radiofrequency ablation causes invasive breast cancer cell death in patients with locally advanced breast cancer. An ongoing study is investigating the use of radiofrequency ablation for the treatment of breast tumors 2 cm or less in diameter.