Bone is the preferentially site of distant colonisation for breast carcinoma (BrCa). BrCa patients with metastases restricted to bone (BO) show a longer overall survival compared with BrCa patients developing bone and visceral metastases (BV). In a gene expression analysis, we found few genes whose expression was significantly different between the two groups of bone metastases. Among them, haemoglobin beta (HBB) was one of the most upregulated in BV vs BO. Based on these data, we evaluated HBB expression in primary human BrCa, finding HBB in 34 out of 57 samples. Moreover, the percentage of HBB positive cancer cells was significantly higher in the invasive lesions than in the in situ counterpart (sixfold, P<0.05). Higher expression of HBB was also observed in ductal infiltrating carcinoma vs the lobular invasive histotype (2.2-fold, P<0.05). Interestingly, a positive correlation (P<0.05) was observed between HBB and the Ki67 score. We next compared HBB expression between poorly aggressive (MCF7, HCC1954) and highly aggressive (MDA-MB-231) BrCa cells, finding a higher expression in the latter. HBB overexpression in MDA-MB-231 (MDA-HBB) and MCF7 (MCF7-HBB) cells increased migration and invasion ability compared with control (MDA and MCF7-empty), along with an increased expression of MMP9. Moreover, MDA-HBB and MCF7-HBB conditioned media induced in vitro tube formation (1.5-fold increase, P<0.05). Consistently, the in vivo growth rate of orthotopically implanted MDA-HBB was higher compared with MDA-empty. Endpoint tumour weight was increased too (1.9-fold, P=0.002), while histology revealed less fibrosis in MDA-HBB and MCF7-HBB-derived tumours (0.4-fold, P<0.001) along with increased angiogenesis. Finally, local recurrence and visceral metastases were observed only in MDA-HBB implanted mice (incidence, 60%). Similar results were observed in MCF7-HBB orthotopically injected mice. Altogether, our findings demonstrate a positive correlation between HBB expression and BrCa aggressiveness, paving the way for the use of HBB as a BrCa progression marker.
Disclosure: The authors declared no competing interests. This work was supported by the Associazione Italiana per la Ricerca sul Cancro (AIRC) (grant number 11950).