Diseases start with cells. Cell tissues create body organs. Normally whenever the body needs, new cells develop and in order to do that they get divided. When the cell gets older and die, they are replaced by the new ones. This is called planned cell death.
Due to the exposure to genetic factors and carcinogenes, some cells can avoid this planned cell death and gain autonomy. These invasive cells, which multiply by dividing into two, use nutrients by seizing the tissue or organ they are in (metastasis) to distant organs. In fact, malignant cells form during herbivorous life. However the protective mechanisms in our bodies catch and destroy them. Diseases emerge when these protective mechanisms are out of balance.