A metastatic lymph node refers to a lymph node that contains cancer cells that have spread from a primary tumor located elsewhere in the body. These small, oval-shaped structures are part of the body’s immune system, which helps filter fluids and fight off infections and diseases, including cancer. The presence of cancer cells in lymph nodes signifies that the disease has begun to spread, a process known as metastasis. This spread impacts how cancer is categorized and the subsequent treatment strategies.
Understanding Lymph Node Metastasis
Lymph nodes are tiny, bean-shaped organs distributed throughout the body, connected by a network of thin tubes called lymph vessels. This network, along with organs like the spleen and thymus, forms the lymphatic system, which filters lymph fluid and houses white blood cells that combat harmful invaders. Lymph fluid, a clear, watery substance, collects waste products, bacteria, damaged cells, and potentially cancer cells from body tissues before draining into the lymph vessels.
Metastasis is the process by which cancer cells break away from their original tumor site and travel to other parts of the body. They can enter the lymphatic system by attaching to the walls of lymph vessels and traveling with the lymph fluid.
Once inside the lymphatic system, these cancer cells are carried to nearby lymph nodes. Some can survive, settle, and begin to grow within a lymph node. These new growths will consist of cells that look like those from the original tumor.
Diagnosing Metastatic Lymph Nodes
Detecting cancer in lymph nodes often begins with a physical examination, where doctors may feel for enlarged or hardened nodes, particularly in accessible areas like the neck, armpits, or groin. However, many lymph nodes are located deep inside the body and cannot be felt, even if they contain cancer. For this reason, imaging techniques are frequently employed.
Imaging scans help assess the extent of any growth. Ultrasound is often an initial imaging test for suspicious lymph nodes, offering a low-cost, non-invasive way to visualize them. If cancer is suspected, more advanced cross-sectional imaging, such as CT (computed tomography) or MRI (magnetic resonance imaging) scans, are performed. These scans help determine the size and location of suspicious nodes.
A PET/CT scan, combining positron emission tomography (PET) with CT, is another advanced imaging study that can help determine if lymph nodes are likely to contain cancer cells. PET/CT is accurate for staging lymph node tumors and detecting metastatic tumors. While imaging can show suspicious areas, a biopsy is generally needed to confirm the presence of cancer cells.
A biopsy involves removing tissue or cells from the suspicious lymph node for examination under a microscope by a pathologist. Fine needle aspiration (FNA) is a common biopsy procedure where a thin needle is inserted into the node, often guided by ultrasound or CT, to draw out cells and fluid. If FNA does not provide a definitive diagnosis, other biopsy types, such as core-needle biopsy, incisional biopsy, or excisional biopsy, may be performed. Pathological examination confirms the diagnosis by identifying cancer cells and can provide details about their characteristics.
Implications for Cancer Treatment and Prognosis
The presence of metastatic lymph nodes plays a role in determining the stage of cancer, which guides treatment decisions and provides information about a patient’s outlook. Cancer staging systems, such as the widely used TNM system, categorize the disease based on the primary tumor’s extent, spread to lymph nodes, and distant metastasis. Lymph node involvement is a factor in this classification.
When cancer cells are found in lymph nodes, treatment plans often become more extensive than just removing the primary tumor. Treatment options can include additional surgery to remove affected nodes, radiation therapy to destroy cancer cells, or systemic treatments like chemotherapy, targeted therapy, or immunotherapy. The specific approach depends on the type of cancer, the number of affected nodes, and the overall extent of the disease.
The involvement of lymph nodes indicates a less favorable prognosis compared to cancer that has not spread. For example, the 5-year relative survival rate for breast cancer is 99% if confined to the breast, but drops to 86% if it has spread to lymph nodes. Similarly, for colon cancer, the 5-year survival rate can decrease from 91% in early stages to 72% with lymph node involvement. The number of cancerous lymph nodes is also a predictor of outcome, with a higher number associated with a less favorable outlook.