Could Pelvic Mass Be Malignant?

Good evening -- I had a supracervical hysterectomy 8 years ago and also kept both ovaries. The uterus was over 4 lbs and was riddled w tumors. I continued to bleed at my monthly cycle since the surgery inspite of 2 attempts at chemical cauterization. A recent TV ultrasound and one done 5 years ago both seem to indicate that a uterus is present. The current thinking is that 1) more of the cervical stump was left than we thought or 2) a large mass has grown in its place. I continue to have my cycle now for 8 years following the surgery. Menarche was at 8 years old. My gyno is comparing the films from 5 years ago to the ones taken last week. Even though I am 55, my hormonal panel shows that I am not in menopause (nor in peri). Here is my question -- how concerning is this pelvic mass? Is malignancy likely? Is surgery a consideration if it has grown or even if it has not? Many thanks for listening to my story.