Epithelium is one of the four types of tissue in the body (the others are muscle, nervous and connective) and covers the outer surfaces of organs and blood vessels, as well as the inner surfaces of cavities in many internal organs.

Most ovarian cancers—approximately 85-90%—fall into this category.  Epithelial ovarian cancer is one of the most common gynecologic malignancies, with 50% of all cases occurring in women older than 65 years.  These cancers are diseases in which malignant (cancer) cells form in the tissue covering the ovary or lining the fallopian tube or peritoneum (the serous membrane lining the cavity of the abdomen and pelvis and covering the abdominal organs) and are called carcinomas.

Fallopian tube cancer (FTC) and primary peritoneal carcinoma (PPC) and epithelial ovarian cancer are often grouped together because they share many similarities, including a similar course of treatment.

Epithelial ovarian cancer is divided into different types:

High-Grade Serous Carcinomas (HGSC)
Serous carcinomas are classified as low-grade and high-grade, with high-grade serous carcinomas the most common type of ovarian cancer—approximately 75% of epithelial ovarian cancer including FTC and PPC fall into this subtype.

High-grade serous carcinoma (HGSC) is the most common type of invasive epithelial ovarian cancer (and includes FTC and PPC), and is diagnosed at advanced stages (defined here as Stage III or Stage IV) 70% of the time. This may be because many of the most common subtypes of high-grade serous cancers may originate in the fallopian tubes, with subsequent cancer in the ovaries a result of the spread from a primary tumor in the fallopian tubes and may explain why these cancers are often detected at an advanced stage. Recent research has found that high-grade serous cancers that begin in the fallopian tubes take on average 6.5 years to progress to the ovaries, and then spreads to other areas quickly.

These advanced carcinomas typically spread to the peritoneum first (lining of the organs of the pelvis and abdomen). This may lead to fluid build-up in the peritoneal cavity (ascites) which can result in abdominal bloating. Epithelial, fallopian tube, and peritoneal cancers usually do not cause early signs or symptoms. When signs or symptoms do appear, such as abdominal bloating, the cancer is often advanced.

Once symptoms do occur, they often go unrecognized, leading to delays in diagnosis. MOCA and other organizations around the world have made great efforts to enhance physician and patient awareness of the occurrence of these nonspecific symptoms to bring diagnosis as quickly as possible.

The most common symptoms of ovarian cancer are:

• Abdominal pain or bloating.
• Early satiety or feeling full quickly.
• Urinary urgency or frequency.
• Changes in bowel habits, such as constipation.

Low-Grade Serous Carcinomas (LGSC)
Low-grade serous carcinomas (LGSC) are more similar to serous tumors of low malignant potential and are quite distinct from high-grade serous carcinomas.  This research finding has led some researchers to hypothesize that low-grade carcinomas are in fact tumors of low malignant potential that have gone undetected and are therefore more developed. These tumors rarely develop into a high-grade serous carcinoma.

Endometrioid
Endometriosis is also a risk factor for Endometrioid tumors.  Regardless of disease stage, these tumors seem to respond to treatment slightly better than serous carcinomas

Mucinous
Mucinous tumors are usually large with a median diameter of 18 to 20 cm and tend to remain confined to the ovaries. These tumors can also be difficult to distinguish from metastatic mucinous tumors from the colon/rectum, appendix, cervix or pancreas.