Other procedures Radiofrequency ablation is a minimally invasive treatments for fibroids. In this technique the fibroid is shrunk by inserting a needle-like device into the fibroid through the abdomen and heating it with radio-frequency (RF) electrical energy to cause necrosis of cells. The treatment is a potential option for women who have fibroids, have completed child-bearing and want to avoid a hysterectomy. Magnetic resonance guided focused ultrasound, is a non-invasive intervention (requiring no incision) that uses high intensity focused ultrasound waves to destroy tissue in combination with magnetic resonance imaging (MRI), which guides and monitors the treatment. During the procedure, delivery of focused ultrasound energy is guided and controlled using MR thermal imaging. Patients who have symptomatic fibroids, who desire a non-invasive treatment option and who do not have contraindications for MRI are candidates for MRgFUS. About 60% of patients qualify. It is an outpatient procedure and takes one to three hours depending on the size of the fibroids. It is safe and about 75% effective. Symptomatic improvement is sustained for two plus years. Need for additional treatment varies from 16 to 20% and is largely dependent on the amount of fibroid that can be safely ablated; the higher the ablated volume, the lower the re-treatment rate. There are currently no randomized trial between MRgFUS and UAE. A multi-center trial is underway to investigate the efficacy of MRgFUS vs. UAE. Prognosis About 1 out of 1,000 lesions are or become malignant, typically as a leiomyosarcoma on histology. A sign that a lesion may be malignant is growth after menopause. There is no consensus among pathologists regarding the transformation of leiomyoma into a sarcoma. Metastasis There are a number of rare conditions in which fibroids metastasize. They still grow in a benign fashion, but can be dangerous depending on their location. See extrauterine fibroids. Epidemiology About 20% to 80% of women develop fibroids by the age of 50. Globally in 2013 it was estimated that 171 million women were affected. They are typically found during the middle and later reproductive years. After menopause they usually decrease in size. Surgery to remove uterine fibroids occurs more frequently in women in "higher social classes". Adolescents develop uterine fibroids much less frequently than older women. Up to 50% of women with uterine fibroids have no symptoms. The prevalence of uterine fibroids among teenagers is 0.4%. Europe The incidence of uterine fibroids in Europe is