Concurrent inhibition of hypoxia caused proteins could help avoid the further distribution of metastatic tumour cells and to limit the development and growth of subclinical tumour metastases. Patients that experience loco local relapse of these primary tumor after radiation therapy frequently develop metastatic infection, and recurrent tumours are generally hypoxic. The potential for long term inhibition of hypoxia induced proteins in patients after primary tumour treatment to prevent the subsequent growth and development of tumour metastases is unknown, even though the importance of proteins, such as LOX and CXCR4, in a number of normal physiological processes may preclude the long term utilization of LOX or CXCR4 inhibitors as prophylactics against metastatic illness. PR 104 can target tumour metastases due to the existence of hypoxic cells in the metastatic tumour foci and/or the generation of cytotoxic PR 104 metabolites by the hypoxia separate enzymatic activity of intracellular a 1C3 expressed by several tumour cell types. Regardless, PR 104 has potential as a hypoxia triggered cytotoxin that targets metastatic tumour cells as well as cells in the primary tumour. Importantly, both TH 302 and PR 104 show pre clinical activity when used as individual agents, which sets these compounds besides early in the day era hypoxia triggered cytotoxins which demonstrate anti tumour activity only once used in combination with radiation or chemotherapy.