Currently as our advanced prostate cancer progresses and we develop bone and soft tissue tumors our pain increases significantly. Current treatment options for the palliation of this pain includes painkillers (including opioids and methadone), radiation and in rare incidents surgery. All of these options have significant limitations.

Drugs eventually become less effective, especially for breakout pain and we are limited to the amount of and the timing of radiation to control the tumor growth.

First-of-its-kind research showed that it might be possible to use microwave ablation (MWA) therapy to control pain. This research showed that it is possible to cut pain in half for patients with painful bone and soft-tissue tumors as well as taking less time to complete than alternative treatment options. In the study pain relief lasted over 4 months on average and up to 15 months in some of the subject patients. Results of this study were reported at the 29th Annual Meeting of the American Academy of Pain Medicine.

The study results appeared in a poster given by investigators from the Centre Hospitalier Universitaire, a university hospital in Besançon, France. The researchers stressed that results are preliminary but said percutaneous MWA treatment may be effective for patients whose pain from bone and soft-tissue tumors has been unrelieved by previous therapies.

“This technique may be applied to any patient suffering from bone tumor pain, mainly in patients suffering from bone metastases, refractory to conventional therapies,” said Adrian Kastler, MD, a resident in Interventional Pain Management and lead author. “The main advantage of ablation techniques is the fast pain relief obtained — immediately after the procedure — as opposed to delayed pain relief obtained with radiation therapy.”

The study was very small, only consisting of 13 patients in whom a total of 20 MWA procedures were performed. It is not clear whether any of the subjects suffered from advanced prostate cancer tumors. Of the 20 lesions, 16 had metastasized to the lungs, thyroid and other locations. Twelve of 15 bone lesions were osteolytic, showing degeneration of bone tissue. Before the procedure, the mean average pain score reported by patients was 7.29 out of a possible 10, as measured by a visual analogue scale (VAS). The lesions ranged in size from 12 mm to 120 mm.

MWA procedure was performed by inserting small probes, guided by CT scan, through the skin directly into a tumor. The probes are then heated, resulting in thermal coagulation of the tissue. The investigators used an Acculis MTA-2 generator, a frequency source of 4.5 GHz and a 17-gauge antenna.

During the procedure, patients received local anesthesia and nitrous oxide. The mean ablation time was 4.85 minutes and ranged from 1 to 13 minutes. Each cycle lasted an average of 30 seconds to 3 minutes, and there was an average of 4.2 cycles per ablation. The energy used was 60 watts on average.

Patients reported immediate pain relief of at least 50% for 19 of the 20 procedures with results lasting for an average of 4.36 months (range 0.5-15months). As with any needle procedure, bleeding or infection at the ablation site was a risk. The researchers reported only 1 complication: a secondary abscess at the site that required drainage.

The actual ablation process can take up to 30 minutes depending on the size of the lesion being treated. This means that more patients could be treated when time is a factor.

Dr. Kastler stressed that there are no manufacturer guidelines regarding bone or soft tissue but said the study demonstrated that the use of a short, low-powered cycle was safe.

Dr. Kassler said that additional study using different levels of intensity and time of ablation is required to set up guidelines which would probably depend on tumor size. Dr. Kassler also indicated that expects the indication to reach beyond palliation.

“Our research showed that the use of MWA in bone and soft-tissue tumors is feasible and effective concerning pain palliation,” Dr. Kastler said. “However, MWA needs to be studied in order to apply the same procedure in a curative intention.”

Poster 193 – Microwave Ablation under Local Anesthesia of Bone and Soft-tissue Tumors: Preliminary Results
American Academy of Pain Medicine

Joel T. Nowak, M.A., M.S.W.