## Most Common Sites of Distant Metastasis in Breast Cancer **Key Point:** Bone is the most frequent site of distant metastasis in breast cancer, occurring in approximately 40–50% of patients with metastatic disease. This is followed by lung, liver, and brain in decreasing order of frequency. ### Pattern of Metastatic Spread | Site | Frequency | Clinical Significance | |------|-----------|----------------------| | Bone | 40–50% | Most common; often osteolytic or osteosclerotic lesions | | Lung | 20–30% | Second most common; may be asymptomatic initially | | Liver | 15–20% | Associated with poor prognosis | | Brain | 10–15% | Late manifestation; associated with HER2+ and triple-negative subtypes | | Pleura | 5–10% | Malignant pleural effusion | **High-Yield:** The "seed and soil" hypothesis explains why bone is the preferred site: breast cancer cells have a natural tropism for the bone microenvironment, which provides growth factors and cytokines that support tumour proliferation. **Clinical Pearl:** Bone metastases in breast cancer are often detected on skeletal scintigraphy or PET-CT and may present with bone pain, pathological fractures, or hypercalcaemia. Patients with bone-only metastases generally have a longer median survival (2–3 years) compared to those with visceral metastases (6–12 months). **Mnemonic:** **BLBL** — Breast cancer metastases go to **B**one, **L**ung, **B**rain, **L**iver (in order of frequency). ### Why Bone? The bone marrow microenvironment is rich in osteoclast-activating factors, TGF-β, and other growth factors that create a permissive niche for breast cancer cell colonisation and dormancy. This explains both the high frequency and the often indolent nature of bone-only disease.
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