In almost all cases, fibroids are benign. The risk of fibroids turning into cancer is less than 1%. If fibroids grow in size rapidly, doctors may consider that there is a risk for cancer transformation. However, when fibroids are removed for this reason, they are rarely found to be cancerous when tested.
There is also a very rare type of ‘cancerous fibroid’ (leiomyosarcoma) that is thought to arise independently, and not develop from a benign fibroid.