ACVRL1 and neoplasm: ACVRL1 (also known as ALK1) is a cell surface receptor in the TGF-beta signalling pathway which binds bone morphogenic protein (BMP)-9 and -10, appears to be involved in developmental and angiogenic blood vessel formation, and has been shown to be highly expressed in the vasculature and stroma in a high proportion of prostate tumours.52 Germline disruptive variants within ACVRL1 could therefore in principle inhibit development of new tumour vasculature and hinder the onset of metastases.