Tumor sleeps

        All higher animals need sleep. Mammalian sleeps regularly. Some animals like bear even take prolonged winter sleep. Reptiles that are unable to keep constant body temperature go into various periods of dormancy depending on the latitude and the local environment. Adders in north Europe have a dormancy of 275 days, whereas adders in south Europe have a dormancy of 105 days. The dormancy period for adders In UK is only two weeks, owing to the warm climate provided by the Gulf Stream. Dormancy is a state of being relative less active and more resistant. It helps organisms to adapt to unfavorable environments.

        Tumors also enter dormancy to avoid certain extreme environments, such as the microenvironment in their early progression, during micrometastases, or after a successful anti-tumor treatment. During early progression, the immune system of the host attempts to nip tumors in the bud. In the process of micrometastases, tumors endure angiogenesis suppression. Right after anti-tumor treatment such as surgery, chemotherapy, or radiation, tumors face even tougher situations caused by invasive procedures or drugs. Some tumors get around these extreme environments by going dormant.

        The phenomenon of tumor dormancy poses many interesting questions: How do we detect sleeping tumors? Can they be killed more easily or will they go rampant if awakened? How is tumor dormancy initiated? If we can take advantage of tumor dormancy, we may be able to switch tumors to dormancy indefinitely so that patients will die with tumors but not of tumor.