Ovarian cancer is the growth of cancer cells in the ovaries. The ovaries make eggs for reproduction and female hormones.

The most common type of ovarian cancer is epithelial. Germ cell tumors come from the reproductive tissue. They account for 20% of tumors. Stromal cancers are more rare. These come from the connective cells of the ovary. They typically make hormones that cause symptoms.

Cancerous Mass in the Left Ovary
Ovarian Cancer
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Cancer occurs when cells in the body divide without control or order. Normally, cells divide in a regulated manner. If cells keep dividing uncontrollably when new cells are not needed, a mass of tissue forms, called a growth or tumor. The term cancer refers to malignant growths. These growths can invade nearby tissues. Cancer that has invaded nearby tissues can then spread to other parts of the body.

It is not clear exactly what causes these problems in the cells, but is probably a combination of genetics and environment.