Vulvar cancer is a rare malignancy that develops on the external female genitalia, most commonly beginning in the labia majora or labia minora. The most prevalent form is squamous cell carcinoma, which originates in the thin, flat cells on the skin’s surface. Metastasis occurs when cancer cells break away from the primary tumor and travel through the body to establish new growths. Understanding the typical pathways of spread is important for diagnosis and treatment planning. The cancer generally follows a predictable route, first involving the regional lymph nodes before potentially reaching more distant organs.
Initial Spread Through the Lymph Nodes
The lymphatic system is the primary initial route for vulvar cancer spread because the vulvar area is rich in lymphatic vessels. These vessels collect fluid and cellular material, including escaped cancer cells, transporting them to nearby lymph nodes for filtering. The first site of potential spread consists of the inguinofemoral lymph nodes located in the groin area.
These nodes are separated into two main groups: the superficial inguinal nodes, which receive drainage directly from the vulva, and the deep femoral nodes situated deeper within the thigh. Cancer cells typically move from the primary tumor to the superficial nodes first, then proceed to the deep femoral nodes. The last of the deep femoral nodes, called Cloquet’s node, acts as a gateway before the cancer can spread further into the pelvis.
The location of the primary tumor can influence the pattern of lymphatic spread, though the intricate network often leads to involvement on both sides of the groin. For tumors located near the midline, such as the clitoris, there is a higher likelihood of bilateral spread. Assessing these regional nodes is a necessary step, as the presence of cancer in the lymph nodes is the most significant factor determining the overall patient outlook.
Surgeons often use a sentinel lymph node biopsy to identify the first node that drains the tumor, aiming to remove fewer nodes and reduce the risk of complications like chronic swelling. If cancer cells are found within these regional lymph nodes, the disease is classified as being in an advanced regional stage. This indicates that the cancer has moved beyond the vulva itself and requires more extensive treatment.
Locations of Distant Metastasis
Once cancer cells move beyond the inguinofemoral and pelvic lymph nodes, they can enter the bloodstream and travel to organs far from the original tumor site. This distant spread is a feature of the most advanced stage of vulvar cancer and is significantly less common than initial lymphatic involvement. When it occurs, the cells typically follow a hematogenous route, meaning they circulate through the blood vessels.
The most frequent site for distant metastasis is the lungs, which are often the first organ affected after the cancer bypasses the regional lymphatics. The liver is the second most common location for these distant growths to develop. Cancer cells can also settle and grow within the skeletal system, leading to bone metastases.
Less frequently, distant spread may involve other tissues, such as non-regional skin or lymph nodes outside the pelvis, like those in the chest or armpit region. Distant metastasis is generally a late event in disease progression, often occurring after the cancer has already recurred locally or spread extensively through the lymphatics. The appearance of disease in these distant locations changes the focus of treatment toward managing the advanced stage of the illness.
Key Factors Affecting Spread Risk
The risk of vulvar cancer spreading is linked to several measurable characteristics of the tumor itself. One important factor is the depth of invasion, which measures how far the tumor has penetrated below the skin surface into the underlying tissue. Deeper tumors have an increased chance of reaching the lymphatic and vascular networks, providing a pathway for cancer cells to escape.
A tumor that has invaded more than one millimeter into the underlying tissue is considered higher risk for lymphatic spread and typically requires a thorough assessment of the lymph nodes. Tumor size is another factor, as larger tumors present a greater volume of cancer cells with more opportunities to enter the circulatory system. Tumors greater than two centimeters in diameter are associated with a higher likelihood of lymph node involvement.
The histological grade of the tumor, which describes how abnormal the cancer cells look under a microscope, also affects the risk of metastasis. Poorly differentiated tumors, referred to as high-grade, look very different from normal tissue and tend to be more aggressive. These aggressive cell types are more prone to rapid growth and have a greater capacity to invade and spread. Some less common types, like verrucous carcinoma, are known for their slow growth and low potential for regional or distant spread.