Cancer is a disease caused by abnormal, uncontrolled proliferation of abnormal cells and spreads to other parts of body either through blood, lymphatic vessels or through direct invasion.
Studies in the past have shown cancer incidence increases with increasing body size among species. In humans, cancer incidence increases with increasing height for numerous cancer types such as colon, malignant melanoma, breast, endometrium, ovary, kidney, CNS, non-Hodgkin lymphoma and leukemia.
However, latest study in elephant showed there is no correlation between body size and cancer risk across species. This phenomenon is called as “Peto’s paradox” and is explained partly through refunctioning of pseudogene called leukemia inhibitory factor (LIF6) .A leukemia inhibitory factor promotes programmed cell death which occurs in controlled and predictable manner. Programmed cell death is considered as a vital component of various processes including normal cell turnover, proper development and functioning of the immune system, embryonic development and chemical-induced cell death.
Researcher called leukemia inhibitory factor; zombie gene as this death gene becomes functional and it kills the cell rapidly in response to DNA damage; thereby preventing the development of cancer.