For any body cell, like we human beings, the complex organism, natural end is death or cytolysis (Pathological breakdown of cells by the destruction of their outer membrane).
But before we approach to death, we display different behaviors through out life, based on our biological and mental age.
We humans, or some of us, exhibit uncontrolled behavior of consumerism. Esp. in young age, before crossing 40s. This consumerism is most selfish pursuit. We just have one thing in mind. I will consume as much I can afford. Who are you to give sermons to me? That is cancerous behavior. Disrespect for society. Disrespect for mother nature. Utter neglect towards natural resources. When a Nation is full of such selfish citizens who hardly performing their duties towards society, nation, Mother Earth, we can declare that there is indeed lump of cancerous citizens.
What causes societal cancer? Lack of moral education in school.
Same is the cause of human body cancer. Lack of I-ness. Lack of morals of living or treating needs of each body cell. When it is neglected, body cells rebels. They outgrow the I-ness you have and establish own identity.
Roots are all mental. Solve your consumerism behavior and cancer will be cured too.