Epithelial Cancers

Epithelial ovarian cancer is the most common type of ovarian cancer.

Epithelial cancers are also called carcinomas. Epithelial ovarian cancer is divided into different subtypes, based on histology, which is the appearance of the tumor cells. The most common type is serous cancer, which may be high or low grade. Less common subtypes are mucinous cancer, endometrioid cancer, or clear cell ovarian cancer. These histological subtypes are associated with different cancer-causing mutations. As a result, treatment recommendations may be tailored for each of these ovarian cancer subtypes.

High-Grade Serous Ovarian Carcinoma (HGSOC)

High-grade serous ovarian carcinoma is the most common type of ovarian cancer — comprising approximately 75% of epithelial ovarian cancers. 

In most people, high-grade serous ovarian carcinoma is diagnosed at advanced stages (stage III or stage IV), meaning that these cancers often spread beyond the ovary or fallopian tube before they are detected.  This is because symptoms associated with HGSOC may be vague and ovarian cancer may not be considered as a possible cause. 

For example, the peritoneum (the lining of the pelvis and abdominal cavity) is a common site of metastasis (spread) by the cancer. Tumor spread to peritoneum may cause fluid build-up in the peritoneal cavity (ascites) which can result in abdominal bloating. These symptoms may only arise once the cancer has already spread beyond the ovaries, and bloating is often attributed to other causes such as gastrointestinal disorders, leading to delays in diagnosis. OCRA and other organizations around the world have made great efforts to enhance physician and patient awareness of the possible association of these nonspecific symptoms with ovarian cancer to hasten diagnosis.

Signs and symptoms associated with ovarian cancer may include the following:

  • Bloating
  • Pelvic or abdominal pain
  • Difficulty eating or feeling full quickly
  • Urinary symptoms (urgency or frequency)

Low-Grade Serous Carcinoma of the Ovary (LGSOC)

Low-grade serous carcinomas of the ovary (LGSOC) are thought to arise from different mutations than high grade tumors. The grade of a cancer refers to the appearance of the cancer cell microscopically.  Low-grade tumors are generally slower growing and less aggressive than high grade cancers.  Although low-grade serous cancers can metastasize, they rarely develop into a high-grade serous carcinoma, and are associated with a better prognosis overall.  

Clear Cell Ovarian Carcinoma (CCOC)

Clear cell ovarian cancers are a rare subtype of EOC. In the US, CCOC make up approximately 6% of all EOC cases, with different frequencies among patient populations:  4.8% in whites, 3.1% in Blacks, and 11.1% in Asians. In Japan, the prevalence of ovarian CCOC is higher, with an estimated incidence of 25% of epithelial ovarian cancers. Endometriosis, a benign condition, may increase the risk of developing clear cell carcinoma. Patients with clear cell carcinoma tend to be diagnosed at a younger age than patients with other types, but this cancer type is also more often found at early stages. Recent research has found that CCOC are associated with different cancer-causing mutations than HGSOC, and these cancers are more resistant to chemotherapy.  As a result, different treatment strategies are under investigation for people with this type of EOC.

Rare Ovarian Cancers: What's New in 2021

For more information on research progress surrounding rare ovarian cancers, watch the video Rare Ovarian Cancers, presented by Dr. Rachel Grisham of Memorial Sloan Kettering Cancer Center at OCRA’s National Conference.

Endometrioid Ovarian Carcinoma

Endometriosis may also be associated with endometrioid ovarian tumors.  Endometrioid carcinomas of the ovary may also be high-grade or low-grade, with low-grade being more common. Treatment of this cancer subtype is similar to treatment of serous EOC.

Mucinous Carcinoma

Mucinous ovarian cancer is a rare kind of epithelial ovarian cancer. Mucinous tumors are usually large with a median diameter of 18 to 20 cm and tend to remain confined to the ovaries. It can sometimes be difficult to distinguish primary ovarian mucinous tumors from metastatic mucinous tumors from the intestines or appendix, but it is important to do so to ensure the most effective treatment. When diagnosed in early stages, prognosis for patients with primary mucinous carcinoma is quite good.

Borderline Ovarian Tumors

Borderline epithelial ovarian tumors are also called tumors of low malignant potential (LMP) because they do not invade adjacent healthy tissue. These tumors are not benign, however, because they can spread to other sites beyond the ovary, and they can recur after surgical resection.  Borderline tumors may be serous, mucinous or endometrioid.  Borderline tumors tend to occur in younger women, and are associated with a better prognosis than invasive cancers.  These tumors account for 15% of all epithelial ovarian cancers, and nearly 75% are diagnosed at Stage 1. 

Symptoms associated with borderline tumors may include the following:

  • Pain or swelling in the abdomen.
  • Pain in the pelvis.
  • Gastrointestinal problems, such as gas, bloating, or constipation.

Prognosis depends primarily on the stage of the disease (whether it affects only the ovary, or has spread to other places in the body). Patients diagnosed with ovarian low malignant potential tumors have a good prognosis, especially when the tumor is found early.