Where does breast cancer commonly metastasize to?

Common Sites of Breast Cancer Metastasis

Breast cancer most commonly metastasizes to bone (51%), followed by liver/soft tissue (19%), pleura (16%), lung (14%), and brain (4%), with metastatic patterns varying significantly by molecular subtype. 1

Metastatic Patterns by Molecular Subtype

Breast cancer metastasis follows distinct patterns based on molecular subtypes:

• Luminal Subtypes (ER/PR positive):

  • Primarily metastasize to bone (82% of bone metastases occur in ER/PR positive tumors) 1
  • Longer survival after metastasis (median 2.2 years for luminal A) 2
  • Long-term risk of recurrence, especially to bone 1

• HER2-Enriched Cancers:

  • Higher rates of liver and lung metastases 1, 2
  • Increased risk of brain metastases 2
  • Shorter survival after metastasis (median 0.7 years) 2

• Triple-Negative/Basal-like Cancers:

  • Preferentially metastasize to liver, lung, and brain 1, 3
  • Significantly lower rate of bone metastases compared to other subtypes 2
  • Poorest prognosis after metastasis (median survival 0.5 years) 2

Clinical Implications of Metastatic Sites

Bone Metastases

• Most common site overall, affecting up to 70% of women with stage IV disease 1
• Complications include pain, pathologic fractures, spinal cord compression, and hypercalcemia 4
• Detected by bone scans with 98% sensitivity for early bone metastasis in symptomatic patients 1

Liver Metastases

• Carries the worst prognosis (median survival of only one month after diagnosis) 5
• More common in HER2-enriched and luminal/HER2 subtypes 2
• Less common in basal-like tumors 2

Lung Metastases

• Identified in 5-9% of asymptomatic women with late-stage breast cancer 1
• Basal-like breast cancers show particular lung tropism 3
• Median survival of approximately 12 months after diagnosis 5

Brain Metastases

• Higher risk in HER2-enriched and triple-negative subtypes 2
• Poor prognosis with median survival of three months after diagnosis 5
• Requires specialized imaging for detection (not typically found on routine staging)

Diagnostic Approach for Metastatic Disease

For patients with late-stage breast cancer (stage IIB-III), evaluation for distant metastases should include:

• Bone scan: Highly sensitive (62-100%) for detecting bone metastases 1
• CT chest, abdomen, and pelvis with IV contrast: Recommended for tumors >2cm (T2) or with positive lymph nodes, or >1cm (T1c) with HER2+ or triple-negative disease 1
• PET/CT: Optional additional test with higher sensitivity (97%) and specificity (91%) compared to conventional imaging 1

Clinical Pearls and Pitfalls

• Pitfall: Assuming all breast cancers have similar metastatic patterns. Always consider the molecular subtype when evaluating for metastases.
• Pitfall: Relying solely on bone scans for metastatic workup. Up to 17.1% of women with extraosseous metastases on CT may have negative or inconclusive bone scans 1.
• Pearl: The presence of peripheral bone metastases almost always (>99%) occurs with extraosseous or central osseous metastases 1.
• Pearl: Metastatic workup for asymptomatic patients is most indicated with T3 or T4 primary lesions, with incidence of stage IV disease at 22% for T3 and 36% for T4 tumors 1.

Understanding the metastatic patterns based on molecular subtypes allows for more targeted surveillance and earlier intervention, potentially improving outcomes for patients with metastatic breast cancer.