How Does a Cancer Start?

It is not entirely known what causes cancer but there are risk factors that may contribute to the likelihood of developing cancer. 

Risk factors that can be controlled include: 

• Smoking
• Exposure to the ultraviolet (UV) radiation in sunlight

Risk factors that cannot be controlled include: 

• Race: certain races have increased risk of certain cancers
• Age: many cancers are seen more often in people of a certain age
• Initial infection with a virus or bacteria
• Genetics: some types of cancer are inherited

Cancer types are named for the organs or tissues in which the cancers form, such as lung cancer, which starts in cells of the lung, and pancreatic cancer, which starts in cells of the pancreas. 

The American Cancer Society estimates the most common cancers in the U.S., excluding nonmelanoma skin cancers, for 2022 will be:

1. Breast cancer
2. Prostate cancer
3. Lung and bronchus cancer
4. Colorectal cancer
5. Melanoma skin cancer
6. Urinary bladder

The American Cancer Society estimates the deadliest cancers for 2022 in the U.S. will be: 

1. Lung and bronchus cancer
2. Colorectal cancer
3. Pancreatic cancer
4. Breast cancer
5. Prostate cancer
6. Liver and intrahepatic bile duct

There are more than 100 types of cancer that can affect almost every part of the body. 

Types of cancer are usually named for the organs or tissues in which the cancers form, such as lung cancer that starts in cells of the lung, and pancreatic cancer that starts in cells of the pancreas. 

Cancers are also named by the type of cells that form them. Some categories of cancers that begin in specific types of cells include: 

• Carcinomas 
  • Carcinomas are the most common type of cancer, formed by epithelial cells that cover the inside and outside surfaces of the body
• Sarcomas
  • These are cancers that form in soft tissues of the body, including muscle, tendons, fat, blood vessels, lymph vessels, nerves, and tissue around joints
• Leukemias
  • These are cancers that begin in the blood-forming tissue of the bone marrow
  • They do not form solid tumors but instead large numbers of abnormal white blood cells build up in the blood and bone marrow
• Lymphomas
  • These cancers begin in lymphocytes (T cells or B cells), disease-fighting white blood cells that are part of the immune system
  • The two main types of lymphoma include Hodgkin lymphoma and non-Hodgkin lymphoma
• Multiple myelomas
  • Also called plasma cell myeloma and Kahler disease, these cancers begin in plasma cells, a type of immune cell
• Melanomas
  • These cancers begin in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its color)
• Brain and spinal cord tumors
  • These types of tumors are named based on the type of cell in which they formed and where the tumor first formed in the central nervous system
• Other types of tumors
  • Germ cell tumors begin in the cells that give rise to sperm or eggs
  • Neuroendocrine tumors form from cells that release hormones into the blood in response to a signal from the nervous system
    • Carcinoid tumors are a type of neuroendocrine tumor usually found in the gastrointestinal system