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The equilibrium phase is often the longest phase of cancer immunoediting and can last many years. In this phase, the cancer cells undergo a period of dormancy, described as a phase of dynamic equilibrium in which tumour outgrowth is suppressed by the immune system. Evidence for equilibrium comes from primary tumorigenesis experiments in which immunocompetent mice were treated with low-dose carcinogens and were found to have occult * cancer cells even though there were no apparent tumours present. When the T cells and IFN-y were depleted in these mice by administering monoclonal antibodies, tumours rapidly appeared at the original site of carcinogenesis injection and were highly immunogenic. Further analysis found that cytokines (e.g., IL-12) and cells (e.g., CD4+ and CD8+ T cells) of the adaptive immune system were responsible for this state of tumour dormancy