Hi and welcome to hcm. Usually ultrasound is accurate in detecting such tumors and most probably this is benign tumor as it says. WOmen who have had breast tumor in their medical history or in family have more chance of suffering from uterine and ovarian tumors. Fibroid or myoma are benign lesions and malignant alteration is extremely rare. It can cause problems if grow up to much and cause bleeding or press surrounding structures. this isnt significant size and I recommend to do frequent check ups and see is there rapid size progression or not. Uterus removal is also option and this is a routine procedure today. So you dont have to worry,cancer would have more intensive symptoms. Wish you good luck.