Prostate cancer begins when cells in the prostate gland grow out of control. While the disease may remain localized, cancer cells can break away from the primary tumor and travel to other parts of the body, a process known as metastasis. The lymphatic system is the most common initial pathway for prostate cancer cells to spread outside the gland. Finding prostate cancer in the lymph nodes signifies that the disease has progressed beyond the prostate itself, which is a significant factor in determining the cancer stage and subsequent treatment strategies.
Understanding How Prostate Cancer Spreads to Lymph Nodes
The lymphatic system is a network of vessels and nodes that manages the body’s fluid balance and functions as part of the immune system. Lymphatic vessels drain fluid and cellular material from tissues, transporting them toward lymph nodes, which act as filters. For prostate cancer, the first sites of spread are typically the regional lymph nodes located within the pelvic area, such as those near the iliac vessels.
Cancer cells detach from the primary tumor and enter nearby lymphatic capillaries, which carry the cells toward the nodes. This movement is often facilitated by biological processes, including the tumor’s ability to stimulate the growth of new lymphatic vessels (lymphangiogenesis). Once a cancer cell reaches a node, it establishes a new growth, termed a lymph node metastasis. The presence of cancer in these regional nodes indicates the disease is no longer confined to the prostate gland, often classifying it as locally advanced disease.
The first lymph node to receive drainage from the tumor is sometimes referred to as the sentinel node. If cancer cells bypass the regional nodes and travel further, they can reach distant lymph nodes, often located outside the pelvis in the retroperitoneum or above the diaphragm. Finding cancer cells in these distant nodes signifies a more widespread disease, classified differently than when cancer is only found in the regional nodes. The extent of lymph node involvement determines the overall prognosis and treatment plan.
Detecting Lymph Node Involvement and Determining Stage
Determining whether prostate cancer has reached the lymph nodes requires specialized diagnostic procedures, as this information is essential for accurate staging. Standard initial imaging techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI), identify suspicious lymph nodes primarily based on size. However, these methods often miss microscopic cancer deposits in nodes that are not yet enlarged.
A newer and more accurate method for staging is the Prostate-Specific Membrane Antigen Positron Emission Tomography (PSMA PET) scan. This scan uses a radioactive tracer that binds to the PSMA protein, which is highly expressed on prostate cancer cells. PSMA PET scans demonstrate superior accuracy in detecting small lymph node metastases compared to conventional imaging, even in nodes that appear normal in size on CT or MRI.
Definitive confirmation of lymph node involvement typically comes from a surgical procedure known as a pelvic lymph node dissection (PLND), or lymphadenectomy. During this procedure, a surgeon removes a collection of lymph nodes from the pelvic region, and a pathologist examines them under a microscope for cancer cells. The status of these nodes is integrated into the American Joint Committee on Cancer (AJCC) TNM staging system, which uses the letter ‘N’ to describe node involvement.
The staging system assigns N0 if no regional lymph nodes contain cancer cells and N1 if regional nodes are involved. Finding cancer cells in the lymph nodes changes the disease classification from localized to either locally advanced (N1) or, if distant nodes are involved, to metastatic disease (M1a). This directly impacts the patient’s prognosis. Pathological information from the lymph node dissection provides the most reliable data for guiding post-operative treatment decisions.
Treatment Approaches When Lymph Nodes Are Affected
When prostate cancer is confirmed in the lymph nodes, the treatment approach shifts from a local therapy strategy to a multi-modal one that targets both the primary tumor site and systemic spread. Since cancer cells have demonstrated the ability to travel through the body, treatment must combine local control measures with therapy that acts throughout the system. Hormone therapy, specifically Androgen Deprivation Therapy (ADT), is a foundational systemic treatment because prostate cancer cells are dependent on androgens (male hormones) for growth.
ADT works by lowering the level of androgens in the body or blocking their action on cancer cells, which slows the growth of the disease, including cells in the lymph nodes. This systemic therapy is often combined with local treatments to maximize cancer control. Local treatments may involve a radical prostatectomy, which removes the prostate gland along with an extended pelvic lymph node dissection to remove involved nodal tissue.
Alternatively, or as a follow-up to surgery, radiation therapy targets the area where the prostate was located (the prostate bed) and the surrounding lymph node regions. Combining radiation with ADT improves long-term outcomes compared to using either approach alone. For more extensive lymph node involvement, or for disease resistant to initial ADT, newer-generation anti-androgens, such as abiraterone or enzalutamide, may be introduced to intensify the systemic attack. This integrated approach is necessary because cancer cells in the lymph nodes are considered a source of further spread.