Ovarian cancer is a malignant tumour that starts in cells of the ovary. Malignant means that it can spread, or metastasize, to other parts of the body.
The ovaries are part of a woman’s reproductive system. They are 2 small, oval-shaped organs. They are on either side of the uterus, or womb, close to the end of the Fallopian tubes. The ovaries make and release eggs. They also make the female hormones estrogen and progesterone.
The ovaries are made up of different types of cells. Epithelial cells make up the outer layer of the ovary, which is called the epithelium. Stromal cells make up the connective tissue that holds an ovary together. Germ cells are reproductive cells. In women, they are egg cells.
Cells in an ovary sometimes change and no longer grow or behave normally. These changes may lead to non-cancerous, or benign, conditions such as cysts. They can also lead to non-cancerous tumours. For example, changes to epithelial cells can lead to serous adenoma or mucinous adenoma, which are non-cancerous tumours. Changes to stromal cells can lead to non-cancerous tumours such as thecoma or fibroma. Changes to germ cells can lead to non-cancerous germ cell tumours.
Sometimes changes to epithelial cells in one or both ovaries can cause tumours of borderline malignancy. This means that the tumours look like cancer, but they haven’t grown into nearby tissues. Examples of tumours of borderline malignancy include serous tumours or mucinous tumours.
In some cases, changes to ovary cells can cause ovarian cancer. There are 3 main types of ovarian cancer. Each type of cancer starts in a different type of cell found in the ovaries.
- Epithelial tumours start in epithelial cells. Cancerous tumours that start from epithelial cells are called epithelial ovarian carcinomas. Serous carcinoma is the most common type of epithelial ovarian carcinoma.
- Stromal tumours start from stromal cells. Granulosa cell tumours are the most common type of stromal tumour.
- Germ cell tumours are cancerous tumours that start in germ cells. These tumours are rare. Examples of germ cell tumours include dysgerminoma and yolk sac tumour.
Another rare type of ovarian cancer that can also develop is called extra-ovarian primary peritoneal carcinoma. These tumours can develop in the peritoneum, which is the membrane that lines the walls of the abdomen and pelvis. It is similar to epithelial ovarian carcinoma, but there is very little or no cancer in the ovary and it isn’t clear where the cancer started.