Ovarian stromal tumors develop from connective tissue cells that hold the ovary together and those that produce the female hormones, estrogen and progesterone. These tumors are quite rare.
According to Web MD, doctors aren’t sure what causes ovarian cancer. However, they have identified several risk factors. These include age (specifically women who have gone through menopause), smoking, obesity, not having children or not breastfeeding, fertility drugs, hormone replacement therapy, family or personal history of ovarian, breast or colorectal cancer.
Unfortunately ovarian cancer often spreads before it is detected. Web MD also reports symptoms of ovarian tumors include pain or bloating in the abdomen; difficulty urinating, or frequent need to urinate; dull ache in the lower back; pain during sexual intercourse; painful menstruation and abnormal bleeding; weight gain; nausea or vomiting; loss of appetite; and feeling full quickly.
Treatments for cancerous ovarian tumors include chemotherapy, radiation and surgery.
https://www.empowher.com/sexual-well-being/content/problems-female-reproductive-system-ovarian-tumors