Ovarian cancer actually refers to several different types of cancer -- more than 30, in fact. The types of ovarian cancer are grouped by the kind of cell where they start.
Your ovaries have three main types of cells, and a tumor can develop in any of them. The three types are:
- Epithelial cells, which cover the surface of your ovary
- Germ cells, which make your eggs (ova)
- Stromal cells, which hold the structure of your ovary together and make the hormones estrogen and progesterone.
Epithelial Tumors
Most cases of ovarian cancer involve tumors that start in the layer of tissue that covers your ovaries. It’s most common in women who have gone through menopause.
Just because your doctor finds an epithelial tumor doesn’t automatically mean you have cancer. Most epithelial tumors turn out not to be cancer. These “benign” epithelial tumors include serous adenomas, mucinous adenomas and Brenner tumors.
If your epithelial tumor is cancer, it’s called a carcinoma. Those are broken down into different subtypes based on certain things doctors can see under a microscope. The four subtypes of carcinoma are:
- Serous (the most common subtype)
- Mucinous
- Endometrioid
- Clear Cell
If the tumor cells don’t look like any of these subtypes, your carcinoma is “undifferentiated.” These have a tendency to grow faster and spread more quickly than tumors from the four subtypes.
Sometimes, your doctor looks at an epithelial tumor under a microscope and can’t clearly tell whether it’s cancer. That’s called a low malignant potential (LMP) tumor, or borderline epithelial ovarian cancer. It’s less life-threatening than other epithelial cancer, because it doesn’t grow as fast and spread the same way.
Germ Cell Tumors
These tumors are most common in women in their 20s. But women of any age can get them. Most tumors that start in germ cells are benign.
There are several subtypes of germ cell carcinomas, and tumors can also be a mix of more than one subtype. There are four main subtypes:
- Teratoma, when viewed under a microscope, looks like the three layers of a developing embryo. The benign version is called a mature teratoma. Immature teratoma is malignant, or cancerous. This type of tumor is very rare and generally found in girls younger than 18.
- Dysgerminoma is the most common form of germ cell cancer, although it’s still very rare. This type of cancer doesn’t grow very fast or spread quickly. Most women who get it are in their teens or 20s.
- The last two subtypes -- endodermal sinus tumor, also known as "yolk sac tumor," and Choriocarcinoma -- grow and spread rapidly, but they are very rare.
Ovarian Stromal Tumors
These types of tumors are often diagnosed earlier than others.
The most common subtypes are granulosa-theca tumors and Sertoli-Leydig cell tumors. Both are rare.
Another subtype, also rare, is called granulosa cell tumor (GCT).
Other Forms
An extremely rare form of ovarian cancer is called small cell carcinoma of the ovary, or SCCO. Most of the women who get it are young. It tends to be fast-growing.
Although it’s not technically an ovarian cancer, primary peritoneal carcinoma (PPC) is very closely related. When doctors look at it under a microscope, it appears the same as epithelial ovarian cancer. During surgery, it looks like epithelial cancer that has spread to the abdomen. One theory is that PPC starts in the cells that line the fallopian tubes, also a part of your reproductive system.
