In the integrative theory, chronic irritations induce tumors with genetic alterations and rapid proliferative ability. Tumor cells reprogram the metabolism and employ aerobic glycolysis to sustain rapid growth. The host provides both the nutrients and exhaust system to support tumor growth via the tumor microenvironment. Under certain conditions, such as aging, diabetes, obesity and a high‑fat diet, the exhaust system is impaired, triggering a metabolic imbalance between the tumor and host. This is similar to a problematic car with an advanced motor with an out‑of‑date exhaust system. The metabolic imbalance causes a metabolic catastrophe, making tumor cells reside in a dismal environment and forcing them to invade, metastasize and undergo necrosis. Tumor necrosis, particularly in metastases, leads to non‑specific systemic inflammation, which is the major cause of cancer‑related mortality. On the whole, the integrative theory views cancer in an integrative manner and proposes that both genetic alterations and tumor‑host interaction as regards metabolism and immunology determine the destiny of the tumor and host. Although cancer is a genetic disease, tumor biology is basically the nature of the host.