Cancerous tumours of the ovary

A cancerous (malignant) tumour can grow into nearby tissue and destroy it. The cancer can also spread (metastasize) to other parts of the body.

Cancerous ovarian tumours are grouped by the type of cells that the cancer starts in. Epithelial cells are found in the tissue that covers each ovary and lines the fallopian tubes and peritoneum (called epithelial tissue). Epithelial ovarian, fallopian tube and primary peritoneal cancers all start in epithelial cells. Most epithelial ovarian cancers are now thought to start in the nearby fallopian tube, but it’s very difficult to find cancer there before it spreads to an ovary.

Germ cell ovarian cancer and stromal ovarian cancer are rare types of ovarian cancer.

Most ovarian cancers are epithelial ovarian cancer. Epithelial ovarian cancer is also called an epithelial ovarian tumour or epithelial ovarian carcinoma.

The following are different types of epithelial ovarian cancer.

Serous carcinoma is the most common type of epithelial ovarian cancer. It can range in size from small to large and can be high or low grade.

High-grade serous carcinoma (HGSC) grows quickly and is more likely to spread in comparison to low-grade serous carcinoma (LGSC). Doctors think it often starts in a fallopian tube and then spreads to 1 or both ovaries. Most serous carcinomas are high grade.

Low-grade serous carcinoma (LGSC) is much rarer than HGSC. These tumours grow very slowly. LGSC is often found in both ovaries, but it’s possible for it to develop in just one.

Clear cell carcinoma is a rare type of ovarian cancer that can start in the endometrium or the ovaries. It’s more commonly diagnosed at an early stage than serous carcinoma.

Endometriosis is a risk factor for clear cell carcinoma. It's found in more than half of people with clear cell carcinoma.

Mucinous carcinoma usually develops in only 1 ovary and can grow to be very large. It’s typically diagnosed at an early stage.

Mucinous carcinoma can be hard to tell apart from cancer that has spread (metastasized) to the ovary from another part of the body, such as the gastrointestinal (GI) tract or pancreas.

Fallopian tube and primary peritoneal cancer are staged and treated the same way as epithelial ovarian cancer. It's very difficult to find these tumours at an early stage. When cancer is only in the fallopian tube or the peritoneum, it often doesn’t cause symptoms or the symptoms seem like other health problems. As a result, these cancers are often diagnosed at a later stage, after they have grown or spread to the ovaries or other areas and start causing more symptoms. At that point, it's hard to tell exactly where the cancer started.

Serous carcinoma is the most common type of fallopian tube cancer. It starts in the epithelial cells that line a fallopian tube. Other types of fallopian tube cancer are very rare. These include endometrioid carcinomas, leiomyosarcomas and transitional cell carcinomas.

Fallopian tube cancer and most epithelial ovarian cancers start in the fallopian tubes. But it’s very rare and often not possible to find cancer there, before it spreads. If cancer is only found in the fallopian tubes, it’s considered fallopian tube cancer. Once cancer has spread to the ovaries, it’s called epithelial ovarian cancer. This is a much more common diagnosis than fallopian tube cancer.

Primary peritoneal cancer is an uncommon cancer that starts in epithelial cells in the peritoneum. Primary peritoneal cancer looks the same as serous carcinoma of the ovary under a microscope, but there is very little cancer in the ovaries –it's mostly in the peritoneum. Primary peritoneal cancer is also called primary peritoneal serous carcinoma or extra-ovarian primary peritoneal carcinoma. It's different from mesothelioma, which can also develop in the peritoneum.

The following types of ovarian cancer are rare:

• germ cell ovarian cancer
• stromal cell ovarian cancer

Germ cell ovarian cancer starts in germ cells, which eventually become egg cells in the ovary. Most germ cell ovarian cancers are diagnosed at an early stage. They usually develop in teenagers or young adults in their 20s. Germ cell ovarian tumours can also be non-cancerous.

Dysgerminomas are the most common type of germ cell ovarian cancer. They can develop in 1 or both ovaries and spread to the abdomen and pelvis (called extraovarian spread). They are often diagnosed at an early stage.

The following are other common types of germ cell ovarian cancer.

Yolk sac tumours (also called endodermal sinus tumours) are the second most common type of germ cell ovarian cancer. They are often found in 1 ovary, but grow quickly and can spread to the other ovary or to the abdomen and pelvis.

Immature teratomas can appear as large palpable masses. They are usually found in 1 ovary, but can spread to the other ovary.

Stromal cell ovarian cancer is also called sex-cord stromal ovarian cancer. It starts in stromal cells that make up the supportive or connective tissue of the ovary (called the stroma). Stromal cells make the sex hormones estrogen and progesterone. Stromal tumours often make too much of these hormones.

Most types of stromal cell ovarian cancer are low grade, so grow slowly and won’t usually spread. They mostly develop in people older than 50, but may also be found in younger people.

Granulosa cell tumours are the most common type of stromal cell ovarian cancer. Most of these tumours are diagnosed at stage 1. They vary in size and can be solid or have cysts.

Granulosa cell tumours are either adult or juvenile:

• Adult granulosa cell tumours most commonly develop during perimenopause.
• Juvenile granulosa cell tumours usually develop in only 1 ovary. They are most often diagnosed in people younger than 30.