Oncogene-induced senescence is an emergency stop mechanism that induces an irreversible cell cycle arrest in damaged or pre-malignant cells in response to activated oncogenes, DNA damage or telomere dysfunction, thus preventing tumourigenesis.We have identified a novel gene-located at a breast cancer risk locus-that induces senescence in a number of primary cell types including endothelial and mammary epithelial cells, and thus may not only modulate senescence in the epithelial compartment of breast tumours but also in the vascular cells.Expression is induced in response to DNA damage in mammary epithelial cells.Protein expression is limited in normal breast tissue, but expression is widespread in both benign neoplasms and invasive ductal carcinomas; however, in certain subtypes of breast tumours both expression and senescence are absent.In endothelial cells, expression is induced by hypoxia via HIF-1 (Hypoxia Inducible Factor) and the protein reciprocally stabilises HIF-1 thus potentiating a feed-forward loop to induce senescence.Low oxygen tensions are found within the tumour microenvironment and senescence may act to restrict tumour angiogenesis and hence tumour growth.It has been suggested that senescence may play a role as important as apoptosis in both tumour progression and treatment; intriguingly, this novel gene may have a multifunctional role in senescence-mediated tumour suppression.