A 52-year-old woman from Delhi presents with a palpable mass in the upper outer quadrant of the right breast. Core needle biopsy confirms invasive ductal carcinoma. During staging workup, a solitary 2 cm lymph node is detected in the axilla on imaging. Which is the most common site of distant metastasis in breast cancer?

Explanation

## Most Common Site 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. ### Frequency of Metastatic Sites | Site | Frequency | Clinical Features | |------|-----------|-------------------| | **Bone** | 40–50% | Most common; osteolytic or osteosclerotic lesions; pain, fractures | | Lung | 20–30% | Second most common; nodules, pleural effusion | | Liver | 15–20% | Hepatomegaly, elevated LFTs, ascites | | Brain | 10–15% | Least common; neurological symptoms, seizures | | Skin/soft tissue | 5–10% | Local recurrence or distant cutaneous metastases | **High-Yield:** The skeleton (particularly spine, pelvis, ribs, and femur) is the preferred site for metastatic breast cancer cells, likely due to the rich vascular supply and favorable microenvironment in bone marrow. **Clinical Pearl:** Bone metastases in breast cancer are often indolent and may be detected incidentally on imaging or present with bone pain, pathological fractures, or spinal cord compression. Bisphosphonates and denosumab are used for bone metastasis management. ### Metastatic Pattern by Breast Cancer Subtype - **Luminal (HR+):** Bone > lung > liver - **HER2+:** Visceral organs (lung, liver, brain) more common - **Triple-negative:** Visceral and CNS metastases more frequent **Mnemonic: BLBL** — **B**one (most common), **L**ung, **B**rain, **L**iver (in order of decreasing frequency in early metastatic disease, though bone remains the single most common site overall).