To which lymph‑node groups does prostate cancer most commonly metastasize?

Prostate Cancer Lymph Node Metastasis Patterns

Primary Regional Lymph Node Groups

Prostate cancer most commonly metastasizes to the obturator (medial external iliac) lymph nodes, followed by external iliac, internal iliac (hypogastric), presacral, and common iliac nodes. 1, 2

The regional pelvic lymph nodes for prostate cancer include all nodes below the bifurcation of the common iliac arteries, with the following specific distribution pattern based on frequency of involvement:

Most Common Sites (in descending order):

• Obturator nodes (medial external iliac): Most frequently involved, found in 75-89% of patients with nodal metastases 3, 4
• External iliac nodes: Second most common, involved in 83% of cases with nodal disease 4
• Common iliac nodes: Affected in 77% of patients with pelvic nodal metastases 4
• Internal iliac (hypogastric) nodes: Involved in 44% of cases 4
• Presacral nodes: Affected in 33% of patients 4
• Lateral external iliac nodes: Involved in 18% of cases, an area that may be missed if only limited dissection is performed 3

Ascending Pathway to Distant Nodes

Prostate cancer spreads to retroperitoneal lymph nodes invariably through the common iliac nodes first—no patients with negative common iliac nodes have positive retroperitoneal nodes. 4

Progression Pattern:

• Lymphatic spread follows a predictable ascending pathway from pelvis to retroperitoneum 4
• Para-aortic/para-caval nodes: Involved in 26-78% of patients with advanced nodal disease, but only when common iliac nodes are positive 3, 4
• Retroperitoneal involvement typically occurs only when patients have at least 5 positive lower pelvic lymph nodes AND positive common iliac nodes 4

Distant Metastatic Nodes (M1a Disease)

Any lymph nodes beyond the regional pelvic groups are classified as distant metastases (M1a), not regional disease. 1, 2

Non-Regional Nodes Include:

• Extrapelvic retroperitoneal nodes (mediastinal, thoracic): Classified as metastatic disease 1
• Supraclavicular nodes: Rare presentation but documented, typically indicates advanced disease with extensive retroperitoneal involvement 5

Clinical Staging Criteria

Lymph nodes ≥1.5 cm in short axis are considered pathologically enlarged and measurable; nodes 1.0-1.5 cm may be pathologic but are considered non-target lesions. 1, 2

Important Distinctions:

• Pelvic nodal disease: Classified as locoregional (N-stage) 1
• Extrapelvic nodal disease: Classified as distant metastases (M1a) 1, 2

Key Clinical Implications

For Surgical Planning:

• Limited obturator-only dissection misses approximately 50% of metastases present 1
• Extended pelvic lymph node dissection should include obturator, external iliac, internal iliac, presacral, and common iliac nodes 1, 4
• Lateral external iliac nodes warrant inclusion in dissection templates given 18% involvement rate 3

For Radiation Planning:

• Pelvic radiation fields should encompass all regional nodal groups including lateral external iliac nodes 3
• Para-aortic nodes are rarely involved without pelvic lymphadenopathy 3
• Midline presacral nodes show 33% involvement and should be included in treatment volumes 4

Risk Assessment:

• Patients with PSA <20 ng/mL, clinical stage <T2b, and Gleason score <7 have <10% risk of lymph node metastasis and may not require surgical staging 1
• Nomograms can help establish individual risk but may underestimate due to stage migration over time 1

Common Pitfalls

• Assuming negative retroperitoneal nodes without assessing common iliac status: Retroperitoneal involvement never occurs without common iliac involvement 4
• Relying solely on imaging for nodal staging: CT and MRI detect only ~40-50% of nodal metastases, with sensitivity for microscopic disease being particularly poor 1
• Performing limited obturator-only dissection: This approach misses half of all metastases 1
• Excluding lateral external iliac nodes from treatment volumes: These nodes are involved in nearly 1 in 5 cases 3