Anatomical distribution of bone metastases in stage IV breast cancer: According to histological subtype.

Background: Bone is the most common site of metastasis in breast cancer, yet limited data exist regarding the precise anatomical distribution of bone metastases by tumor subtype.

Aim: To examine the anatomical distribution of the first bone metastases in stage IV breast cancer, stratified by histological subtype. Secondary objectives include analyzing the anatomical distribution of subsequent bone metastases, Metastasis-Free Survival (MFI), Progression-Free Interval (PFI), and overall survival (OS).

Methods: A retrospective cohort study was conducted on 107 adult females with stage IV breast cancer and bone metastases between 2013 and 2023. Patients were classified by histological subtype (Luminal A/B, HER2-enriched, and Triple-Negative). First and subsequent bone metastasis locations were identified via computed tomography, positron emission tomography/CT, or magnetic resonance imaging. Survival analyses included MFI, PFI, and OS.

Results: Rib metastases were significantly more common in HER2-enriched tumors (80%, P = 0.041), while scapula/clavicle metastases were more prevalent in Triple-Negative cases (37.5%, P = 0.003). Subsequent bone metastases mirrored initial patterns, with pelvic involvement notably higher in HER2-enriched (60%) and luminal B (58%) patients (P = 0.046). No significant differences were found in MFI, PFI, or OS among subtypes. Receptor-based analysis showed no significant variation in bone metastasis locations.

Conclusion: Breast cancer subtypes are associated with suggestive bone metastasis patterns-specifically, rib involvement in HER2-enriched and scapula/clavicle in Triple-Negative cases. While anatomical variations exist, they did not translate into differential survival or fracture risk in this cohort.