of Ovarian Cancer

Ovarian cancer is a common malignancy in women in the United States, with about 23,000 individuals diagnosed each year.1 The ovaries are small female reproductive organs that reside in the pelvis. The ovary makes female hormones and stores all of the egg cells, which are released once a month during ovulation. There are two ovaries, one on each side of the uterus, or womb. Egg cells are delivered from the ovaries to the uterus by hollow organs called fallopian tubes.

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Some ovarian tumors are benign (not cancerous). Malignant (cancerous) ovarian tumors can originate from the surface epithelium (cells covering or lining the ovaries), germ cells (cells that are destined to form eggs), or sex cord-stromal cells (cells that secrete hormones and connect the different structures of the ovaries). The majority of ovarian cancers develop from cells in the lining of the ovary. These are referred to collectively as epithelial ovarian cancers. In this treatment overview, the term ovarian cancer refers to epithelial ovarian cancer. Benign ovarian tumors and ovarian germ cell tumors are not further discussed in this section.

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Common Epithelial Tumors: Common epithelial cancers that start in the surface epithelium account for the majority of ovarian cancers and include the following types:

  • Serous: This is the most common type of ovarian cancer and accounts for about 40% of common epithelial cancers. It occurs most often in women between the ages of 40 and 60.
  • Endometrioid: This type of ovarian cancer accounts for about 20% of common epithelial cancers and is associated with endometriosis in 5% and endometrial carcinoma (cancer of the womb) in 20% of cases. It occurs most often in women between the ages of 50 and 70.
  • Mucinous: Mucinous cancers account for 6-10% of common epithelial ovarian cancer and most often affect women between 30 to 50 years of age.
  • Clear Cell Carcinoma: Clear cell carcinomas account for about 5% of common epithelial tumors and most often affect women between age 40 and 80.
  • Undifferentiated Cancers: The remaining 15% of common epithelial cancers are referred to as undifferentiated tumors because their exact cell of origin cannot be determined under a microscope.

Borderline Ovarian Tumors: These ovarian tumors of low malignant potential are a subgroup of common epithelial tumors that occur in 10-15% of cases. These tumors are between cancerous and non-cancerous in nature. They originate on the surface of the ovary, but do not invade deeper tissues of the ovary. They have a better prognosis (prediction about the possible outcome of a disease) and cure rate than invasive ovarian tumors.2,3.4

Next: Symptoms & Signs of Ovarian Cancer


1 American Cancer Society. Cancer Facts & Figures 2017.

2 Chobanian N, Dietrich CS. Ovarian Cancer. Surgical Clinics of North America. 2008; 88:285-99, vi.

3 Ries LAG, Melbert D, Krapcho M, Stinchcomb DG, Howlader N, Horner MJ, Mariotto A, Miller BA, Feuer EJ, Altekruse SF, Lewis DR, Clegg L, Eisner MP, Reichman M, Edwards BK (eds). SEER Cancer Statistics Review, 1975-2005, National Cancer Institute. Bethesda, MD, http://seer.cancer.gov/csr/1975_2005/, based on November 2007 SEER data submission, posted to the SEER web site, 2008.

4 Armstrong, D. Ovaries and fallopian tubes. In: Abeloff MD ed. Abeloff’s Clinical Oncology, 4th Philadelphia: Churchill Livingstone, 2008: 1827-50.