What are the most common sites of metastasis in an elderly patient with metastatic prostate cancer?

Most Common Sites of Metastasis in Prostate Cancer

Bone is overwhelmingly the most common site of metastasis in prostate cancer, occurring in 84% of metastatic cases, followed by distant lymph nodes (10.6%), liver (10.2%), and lung (9.1%). 1, 2

Primary Metastatic Sites (in Order of Frequency)

Skeletal Metastases (84%)

• Bone metastases represent the dominant pattern of spread in metastatic prostate cancer, occurring in the vast majority of patients with advanced disease 1, 2
• Approximately 65-75% of elderly patients with advanced prostate cancer will experience at least one skeletal-related event (SRE) during their disease course 3
• SREs include pathological fractures, spinal cord compression, need for radiation or surgery to bone, and hypercalcemia 3
• Without treatment, patients experience an SRE every 3-6 months on average 3
• Bone scintigraphy remains the standard imaging modality for detecting skeletal metastases 1

Distant Lymph Nodes (10.6%)

• Extrapelvic lymph nodes (retroperitoneal, mediastinal, thoracic) are classified as metastatic M1a disease 1
• Among patients with lymph node metastases, 43.4% have multiple metastatic sites involved 2
• Lymph nodes ≥1.5 cm in short axis are considered pathologically enlarged and measurable 1

Liver (10.2%)

• Hepatic metastases occur in approximately 10.2% of metastatic cases 4, 2
• Among patients with liver metastases, 76.0% have multiple metastatic sites involved 2
• When bone metastases are present, liver is the most common site of secondary metastases (39.1%) 2
• Isolated hepatic metastasis without bone involvement is rare but can occur 5

Lung/Thorax (9.1%)

• Pulmonary metastases occur in approximately 9.1% of metastatic prostate cancer patients 4, 2
• Prevalence is about 7% in castration-resistant prostate cancer trials 4
• Among patients with thoracic metastases, 76.7% have multiple metastatic sites involved 2
• When bone metastases are present, thorax is the second most common site of secondary metastases (35.2%) 2

Less Common Sites

• Brain metastases: 12.4% of patients with bone metastases develop secondary brain involvement 2
• Adrenal glands: Less common but detectable on imaging studies 4
• Digestive system: 52.2% of patients with digestive system metastases have multiple sites involved 2
• Kidney and adrenal glands: 76.4% of patients with these metastases have multiple sites involved 2

Critical Clinical Patterns

Multiple Metastatic Sites

• Overall, 18.4% of patients with metastatic prostate cancer have multiple metastatic sites involved 2
• Only 19.4% of men with bone metastases have multiple sites involved, indicating bone-only disease is common 2
• Conversely, patients with visceral or atypical metastases are much more likely to have multiple sites involved (ranging from 43.4% to 76.7% depending on the organ) 2

Prognostic Implications

• The presence of visceral metastases indicates more aggressive disease and poorer prognosis compared to bone-only metastases 1, 4
• Patients with castration-resistant prostate cancer and bone metastases have a median survival of <2 years 1
• The development of SREs dramatically worsens prognosis: median survival drops from 16 months with bone metastases alone to only 7 months when SREs occur 3

Recommended Imaging Strategy

For Initial Metastatic Workup

• Contrast-enhanced CT of chest, abdomen, and pelvis with ≤5 mm axial slices is recommended for all metastatic patients to assess nodal and visceral disease 1
• Bone scintigraphy (may include SPECT for improved characterization) for detecting skeletal metastases 4
• PSMA PET/CT has significantly superior accuracy compared to conventional imaging for detecting visceral metastases and is now the preferred imaging modality when available 1

Common Pitfalls to Avoid

• Bone metastases may paradoxically appear worse on imaging despite effective treatment (flare phenomenon), leading to false interpretation of disease progression 1, 4
• A single negative imaging study does not definitively rule out metastatic disease when clinical suspicion is high 1
• The lack of skeletal involvement does not exclude the possibility of distant metastases in atypical sites 6
• PSA may not be a reliable marker of disease status in patients on androgen deprivation therapy, making imaging crucial for monitoring 4