Can fibroids turn cancerous?

Very very rarely: Given that fibroids are common and leiomyosarcoma of the uterus is very rare, the liklihood of a fibroid turing cancerous is very remote.

No: Fibroids are extremely common and are not cancers. They do not become cancers. There is a cancer (leiomyosarcoma of the uterus) that can look like a fibroid, but is very rare.

Very Rare: Estimates are ~40% women have fibroids of uterus at some point in their reproductive years where estrogen makes them grow. Cancerous change, called leiomyosarcoma, is very, very rare. Even when surgery is necessary to address symptoms such as heavy periods or pelvic pain, less than 1 in 1000 are reported as malignant. Bottom line: no symptoms, no surgery.