In malignant urogenital tumors, tissue oxygenation is compromised and very heterogeneous,with steep and fluctuating spatio-temporal oxygen gradients signaling a complex instability in tumor oxygenation (complex "4D-heterogeneity"). Tumor hypoxia is highly dynamic, and rapidly changing pO(2) gradients may be key factors driving hypoxia-dependent adaptive processes leading to malignant progression. The grand median oxygen tension in malignant urogenital tumors is 7-11 mmHg. In contrast, benign leiomyomas of the uterus are severely, but uniformly, hypoxic with only shallow oxygen gradients ("static hypoxia"). In these benign tumors, the median pO(2) is 1 mmHg and signs of hypoxia-driven processes are missing.