Epithelial ovarian cancer originates in the thin layer of cells covering the surface of the ovary or the lining of the fallopian tube. This type of cancer accounts for the vast majority of ovarian cancer diagnoses, representing about 85% to 90% of all cases. It is considered the second most common gynecological cancer, following uterine cancer.
Fallopian tube cancers and primary peritoneal cancers are now recognized as types of epithelial ovarian cancer due to their shared characteristics and similar treatment approaches. The peritoneum is a thin tissue layer that lines the abdomen and covers internal organs.
Subtypes of Epithelial Ovarian Cancer
Epithelial ovarian cancer includes several distinct subtypes. The most common subtype is high-grade serous carcinoma (HGSOC). HGSOC cells grow and spread quickly, often originating in the fallopian tubes before spreading to the ovaries and beyond.
Other less common subtypes include endometrioid, clear cell, and mucinous carcinomas. Endometrioid carcinoma is sometimes linked to endometriosis and is often diagnosed at earlier stages. Clear cell carcinoma can also be associated with endometriosis. Mucinous carcinoma is characterized by tumors containing abnormal mucus-secreting cells.
Associated Risk Factors and Symptoms
Several factors can increase a person’s likelihood of developing epithelial ovarian cancer. Genetic predispositions play a role, with mutations in the BRCA1 and BRCA2 genes being the most well-known. These mutations also raise the risk of breast cancer. Lynch syndrome, an inherited condition caused by mutations in DNA mismatch repair (MMR) genes, also increases the risk of ovarian cancer, along with colorectal and endometrial cancers.
Other risk factors include increasing age, with most diagnoses occurring in women over 65. A family history of ovarian cancer, even without known genetic mutations, elevates individual risk. Nulliparity (never having been pregnant) is another factor associated with a slightly increased risk. Endometriosis is also considered a risk factor for certain subtypes like endometrioid and clear cell carcinomas.
Symptoms of epithelial ovarian cancer are often vague and can be mistaken for less serious conditions. Common symptoms include persistent bloating or an increase in abdominal size, discomfort or pain in the pelvic or abdominal area, and difficulty eating or feeling full quickly.
Urinary changes, such as needing to urinate more frequently or urgently, are also reported. Other symptoms can include fatigue, changes in bowel habits like constipation or diarrhea, unexplained weight loss, and indigestion.
The Diagnostic and Staging Process
Diagnosing epithelial ovarian cancer involves tests, starting with a physical and pelvic examination to check for any unusual changes or lumps. Imaging tests, such as a transvaginal ultrasound, are frequently used to visualize the ovaries and pelvic organs, helping to identify tumors and determine if they are solid or fluid-filled cysts. A computed tomography (CT) scan may also be performed to look for cancer in the pelvis, abdomen, and lymph nodes, and to assess potential spread to other organs.
A blood test for cancer antigen 125 (CA-125) measures a protein that can be elevated in over 80% of advanced ovarian cancers and 50% of early-stage cases. While useful for monitoring treatment response and recurrence, CA-125 alone is not a definitive screening tool because its levels can also be elevated by benign conditions. A definitive diagnosis of ovarian cancer is only made through a biopsy, which involves surgically removing tissue samples for examination under a microscope by a pathologist.
Staging is an important step that determines the extent of the cancer’s spread and guides treatment planning. The International Federation of Gynecology and Obstetrics (FIGO) system is commonly used, classifying ovarian cancer into four main stages:
- Stage I cancer is confined to one or both ovaries or fallopian tubes.
- Stage II indicates that the cancer has spread beyond the ovaries and fallopian tubes to other organs within the pelvis, such as the uterus or bladder.
- Stage III signifies that the cancer has spread outside the pelvis to the abdominal lining or to lymph nodes.
- Stage IV, the most advanced stage, means the cancer has spread to distant organs like the lungs or liver.
Common Treatment Modalities
Treating epithelial ovarian cancer involves a combination of approaches based on the cancer stage and overall health. Surgery is a primary treatment method, aiming to remove as much of the tumor as possible through a procedure called debulking or cytoreduction. The goal of optimal debulking is to remove all visible cancerous implants, as this is associated with improved outcomes. The extent of surgery can vary, potentially including removal of the ovaries, fallopian tubes, uterus, omentum (a fatty tissue layer in the abdomen), and affected lymph nodes or other abdominal organs where cancer has spread.
Chemotherapy is often given following surgery, known as adjuvant chemotherapy, to destroy any remaining cancer cells. In some cases, chemotherapy may be given before surgery, a strategy called neoadjuvant chemotherapy, to shrink large tumors. Common chemotherapy regimens involve a combination of platinum-based drugs, such as carboplatin or cisplatin, and a taxane, like paclitaxel, delivered intravenously in cycles over several weeks.
Targeted therapy focuses on specific molecular pathways involved in cancer growth. PARP inhibitors are a class of targeted drugs that have shown effectiveness, particularly for patients with BRCA gene mutations. These inhibitors work by blocking DNA repair mechanisms in cancer cells, leading to their death. PARP inhibitors are often used as maintenance therapy after chemotherapy, especially in patients with BRCA mutations, to help prevent cancer recurrence.