Uterine fibroids can be caused due to abnormal growth of muscular cell in the inner wall (myometrium) of the uterus. The fibroid is made from muscular and fibrous tissue. Gene mutations have been discovered lately to cause the cells to grow at an abnormal rate.
Other suspected causes of uterine fibroids may be environmental. Apart from this, hormones, such as estrogen and progesterone which are responsible for preparing the inner uterine wall tissue for the onset of pregnancy, are also suspected to help the growth of fibroids.
It is important to remember that uterine fibroids have not been discovered to become malignant in latter stages, but stay benign.