Ovarian cancer is the second most common gynecologic malignancy and a leading cause of cancer-related death among women. The disease often spreads beyond the ovary before diagnosis, typically disseminating within the abdominal cavity or through the lymphatic system. Metastasis, the spread of cancer cells from the primary tumor, frequently uses the network of lymph vessels. Understanding which lymph nodes are involved is important for determining the extent of the disease and planning effective treatment.
The Primary Lymphatic Drainage Pathways
The lymphatic drainage of the ovaries follows distinct pathways, which dictate the first set of lymph nodes, or sentinel nodes, where cancer cells are likely to travel. One primary route follows the ovarian vessels through the suspensory ligament. This pathway leads directly to the para-aortic and paracaval lymph nodes, located along the aorta and vena cava in the back of the abdomen. This is considered the most common and direct route of spread.
A second major pathway runs along the proper ovarian ligament toward the pelvic region. This route involves the pelvic lymph nodes, including the external iliac, internal iliac, and obturator nodes. Cancer cells can travel through either or both systems, resulting in positive nodes in the abdomen, the pelvis, or both. Approximately 50% of lymph node metastases are found in the para-aortic/paracaval area, 20% in the pelvic area, and 30% in both.
A third, less common drainage route involves the round ligament of the uterus, leading to the inguinal lymph nodes in the groin area. Spread to the inguinal nodes is rare but may occur if the tumor is large or involves the lower reproductive tract. These three anatomical pathways—abdominal, pelvic, and inguinal—must be considered when surgically assessing the extent of the cancer. The spread pattern is consistent whether the cancer originates in the ovary or the fallopian tube, as the lymph vessels follow the same ovarian pathways.
Significance of Lymph Node Involvement in Staging
The presence of cancer cells in the lymph nodes is a defining factor in determining the stage of ovarian cancer, classified using the International Federation of Gynecology and Obstetrics (FIGO) staging system. Nodal status helps predict disease progression and influences treatment choice. The tumor is classified as Stage III if it has spread to the retroperitoneal lymph nodes (para-aortic and pelvic groups), even if the cancer has not spread widely to other organs.
Stage IIIA1 is assigned when cancer has only spread to the retroperitoneal lymph nodes, but not to the peritoneum outside the pelvis. This stage is further divided based on metastasis size: IIIA1(i) indicates deposits 10 millimeters or less, and IIIA1(ii) for those greater than 10 millimeters. Positive lymph nodes are a direct indicator of advanced disease, even when the primary tumor appears confined to the pelvis.
Identifying lymph node metastasis triggers a change in the therapeutic approach, often necessitating a systemic lymphadenectomy (surgical removal of affected node groups). This procedure removes cancer and obtains detailed information for accurate staging. Although lymphadenectomy can lead to side effects like lymph fluid accumulation, the information gained is foundational for staging and treatment planning, often leading to recommendations for additional therapy, such as adjuvant chemotherapy.
Detecting Lymph Node Spread
Initial assessment for detecting lymph node spread often relies on imaging modalities, most commonly computed tomography (CT) scans and sometimes positron emission tomography (PET) scans. These tests are performed before surgery to visualize enlarged lymph nodes that might contain cancer cells. Imaging has limitations because it primarily detects physically enlarged nodes, which may miss microscopic metastasis.
Studies indicate that CT scans have limited ability to detect lymph node metastases due to low sensitivity, often missing cancer in nodes that appear normal in size. The most definitive method for confirming lymph node involvement is surgical assessment, typically conducted during the main tumor removal operation. This involves a lymphadenectomy (removing the nodes) or a sentinel lymph node (SLN) biopsy.
In the SLN procedure, a dye or radioactive tracer is injected near the primary tumor, traveling to the first lymph nodes in the drainage pathway. These “sentinel nodes” are removed and examined for cancer cells. If the sentinel nodes are clear, the likelihood of finding cancer in other nodes is very low, potentially preventing the need for a more extensive lymphadenectomy and associated complications.