Cancer is a disease that causes cells to divide out of control. Normally, the body has systems that prevent cells from dividing out of control. But in the case of cancer, these systems fail. Cancer is usually caused by mutations. Mutations are random errors in genes. Mutations that lead to cancer usually happen to genes that control the cell cycle. Because of the mutations, abnormal cells divide uncontrollably. This often leads to the development of a tumor. A tumor is a mass of abnormal tissue. As a tumor grows, it may harm normal tissues around it. Anything that can cause cancer is called a carcinogen . Carcinogens may be pathogens, chemicals, or radiation.
Mark had smoked a pack of cigarettes every day for 20 years. He tried to quit smoking several times but had never been successful until now.  Recently Mark had been having trouble breath and gone to the doctors. Mark's doctor found a tumor on his left lung.
Are Mark's genes normal or mutated?