Hypoxia is an unfavourable factor which predisposes both to more aggressive disease course and frequent metastases as well as patients’ resistance to standard therapy procedures. The development of neoplasm is dependent on oxygen amount and nutritive products supplied by the new blood vessels’ network (angiogenesis) with following direct distant metastases formation by new lymphatic vessels (lymphangiogenesis). This statement constitutes a paradigm. Hypoxia is a pathophysiological factor for angiogenesis and lymphangiogenesis in the neoplastic tumor. According to the latest clinical research, it was confirmed that hypoxia is a fundamental problem in radiotherapy and low cell’s oxygen saturation accelerates neoplasm progression in spite of the cancer therapy used. Hypoxia might cause drug-resistance through the amplification of specific genes as well as the induction of stress-proteins related to hypoxia.