Bone Abstracts

Breast cancer (BrCa) patients with metastases restricted to bone (BO) show a longer overall survival compared to BrCa patients developing bone and visceral metastases (BV). To unveil the molecular mechanisms that segregate these two BrCa patient groups, we performed microarray analyses on bone metastasis samples from BO and BV patients, finding in the latter a set of up-regulated genes involved in oxygen metabolism. We focused on Hemoglobin B (HBB) and evaluated its expression in human BrCa samples by immunohistochemistry. In ductal infiltrating carcinoma the percentage of HBB positive cells was significantly higher in the invasive lesions than in the in situ counterpart. A higher expression of HBB was also observed in ductal infiltrating carcinoma vs the lobular invasive histotype, while benign lesions, the in situ counterpart of lobular carcinoma and normal tissue were negative. We also observed a positive correlation between HBB expression and the Ki67 proliferation marker. We next compared the expression of HBB between poorly aggressive (MCF7, HCC1954) and highly aggressive (MDA-MB231) BrCa cells, finding a higher transcriptional and protein expression in the latter. MDA-MB231 cells overexpressing HBB (MDA-HBB) showed an increased ability to migrate and invade in vitro compared to control cells (MDA-empty). Orthotopic injection in nude mice revealed a greater ability of MDA-HBB cells to grow in the primary site compared to MDA-empty-injected mice, while histology showed less fibrosis in MDA-HBB tumour sections. Moreover, local recurrence and visceral metastases were observed in three and two over five MDA-HBB injected mice, respectively, while MDA-empty tumour relapse did not occur over the same timeframe. Our results demonstrate a positive correlation between HBB expression and BrCa cell aggressiveness, paving the way for a possible use of HBB as a novel marker for BrCa progression.