Where does breast cancer typically metastasize?

Breast Cancer Metastasis Sites

Bone is the most common site of breast cancer metastasis (51% of cases), followed by liver/soft tissue (19%), pleura (16%), lung (14%), and brain (4%). 1

Primary Metastatic Sites and Frequency

• Bone metastases occur in up to 70% of women with stage IV breast cancer, making it the predominant site of distant spread 2
• Lung metastases are the second most common site at 17% of first metastatic presentations 3
• Brain metastases occur in approximately 16% of cases as the first site of distant disease 3
• Liver metastases are less common as the initial site (6%), but approximately 50% of patients with stage IV disease will eventually develop liver involvement during their disease course 4

Metastatic Patterns by Molecular Subtype

The molecular subtype of breast cancer significantly influences where the cancer will spread:

Luminal (ER/PR Positive) Cancers

• Predominantly metastasize to bone, with 82% of patients who develop bone metastases having either ER and PR or ER positivity in the primary tumor 1
• Carry a long-term risk of recurrence, especially to bone, with up to 13.6% of women diagnosed with early-stage disease developing bone metastasis within 15 years 2, 1
• Even low-grade luminal tumors can metastasize to bone 2

HER2-Enriched Cancers

• Preferentially spread to liver and lung 1
• Have a higher rate of recurrence in the first 4 years compared to luminal subtypes 1
• May have better outcomes with brain metastases when treated with targeted therapies 4

Triple-Negative/Basal-Like Cancers

• Commonly metastasize to liver and brain 1, 5
• Show no predilection for bone metastases, unlike other subtypes 2, 1
• Display lung tropism of metastasis 5
• Have a higher rate of recurrence in the first 4 years 1

Clinical Implications by Metastatic Site

Bone Metastases

• Tc-99m bone scans have 98% sensitivity for detecting early bone metastasis in symptomatic patients 2, 1
• The sensitivity of whole body bone scans for detecting bone metastases in late-stage disease ranges from 62% to 100% 2
• Median survival after bone metastasis is approximately 12 months 3

Lung Metastases

• In asymptomatic women with late-stage breast cancer, metastatic disease to the thorax is identified in 5% to 9% of patients 2
• Median survival after lung metastasis is approximately 12 months 3

Brain Metastases

• Breast cancer is second only to lung cancer as a cause of intracerebral metastases 2
• Brain metastases are rare at initial diagnosis, particularly in stage I disease 2
• Median survival after brain metastasis is only 3 months 3
• The presence of multiple metastatic sites including brain significantly reduces survival compared to single-site metastasis 4

Liver Metastases

• Carries the worst prognosis among all metastatic sites 2, 3
• Median survival after liver metastasis is only 1 month without intervention 3
• With multimodal treatment including surgical resection in selected patients, median survival ranges from 3 to 15 months 4

Important Clinical Pitfalls

• Peripheral bone metastases are almost always (>99%) accompanied by extraosseous or central osseous metastasis, and their detection rarely changes management 2
• False-positive rates on chest CT requiring additional imaging range from 10% to 33% in asymptomatic women 2
• For patients with multiple metastatic sites (liver, brain, and spine), median survival is typically 3 to 15 months depending on cancer subtype and performance status 4
• The presence of multiple metastatic sites carries a median survival of 7.5 months 3