Hi and welcome to HCM.
It usually very difficult to determine is ovarian cyst
malignant or benign. These cysts are most commonly benign and it is recommended to do frequent check ups and evaliat dynamics of growing. Malignancies grow much faster and infiltrate surroundsing tissues. There is really no better approach then it was recommended in your case. There is a possiblity of laparoscopic biopsy
but it is invasive. I suggest to do this ultrasounds and if something suspicous is founds then it can be easily removed. CA125 is confusing many woman. This is a tumour marker, but is also found in endometriosis
, benign cysts, PID and some other intraabdominal tumours and disorders. Wish you good health.