What Is the Number 1 Leading Cause of Cancer?

Cancer refers to a complex group of individual diseases characterized by the development of abnormal cells that divide uncontrollably and can infiltrate and destroy the normal body tissue.

Cancer refers to a collection of a large number of diseases characterized by the development of abnormal cells that divide uncontrollably and can infiltrate and destroy the normal body tissue.

Cancer can often spread throughout your body. It develops when the body’s normal growth control mechanisms stop working. Unlike normal body cells, cancer cells are immortal. These extra cells continue to multiply and may form a mass of tissue called a tumor. Moreover, these cells compete with the normal body cells for nutrition and oxygen and cause starvation of the normal cells.

Some types of cancer, such as leukemia, do not form tumors. Leukemia is the second leading cause of death in the world. Survival rates are improving for many types of cancer because of improvements in cancer screening and cancer treatment. Cancer does not have one single cause. There are usually multiple causes and risk factors involved.

There are over 200 types of cancers.

Cancer may occur anywhere in the body. In women, breast cancer is one of the most common. In men, it’s prostate cancer. Lung cancer and colorectal cancer affect both men and women in high numbers.

There are five main categories of cancer:

1. Carcinoma: It begins in the skin or tissues that line the internal organs.
2. Sarcoma: It develops in the bone, cartilage, fat, muscle, or other connective tissues.
3. Leukemia: It begins in the blood and bone marrow.
4. Lymphoma: It arises from the immune system.
5. Central nervous system cancer: It develops in the brain and spinal cord.

The following table (National Cancer Institute 2022) gives the estimated numbers of new cases and deaths for each common cancer type:

The three most common cancers in men, women, and children in the U.S. are as follows:

• Men: Prostate, lung, and colorectal
• Women: Breast, lung, and colorectal
• Children: Leukemia, brain tumors, and lymphoma

For more information, read our full medical article about cancer signs, symptoms, treatment, and prognosis.

Cancer is caused by changes (mutations) in the DNA within the cells. The DNA inside the cell is packaged into many individual genes, each of which contains a set of instructions telling the cell what functions to perform and how to grow and divide. Errors in the instructions can cause the cell to stop its normal function and may allow it to become cancerous.

A gene mutation can instruct a healthy cell to

• Allow rapid growth
• Fail to stop uncontrolled cell growth
• Make mistakes when repairing DNA errors

Nonmodifiable risk factors include

• Genetic inheritance: Many types of cancer run in the family. The reason may be a faulty gene. For example, BRCA mutation is associated with familial breast cancer.
• Familial cancer syndrome: Some types of syndrome such as Von Hippel–Lindau and familial polyposis coli may be responsible for cancer development in the family.
• Age: As a rule, the risk of cancer increases as you age. This may be because of the inability of a mutated cell to repair itself in old age.

Exposure to any predisposing factors (modifiable risk factors) such as

• Smoking
• Alcohol
• Radiation exposure (diagnostic, occupational, or therapeutic)
• Viruses (human papillomavirus)
• Carcinogens (cancer-causing chemicals such as many industrial solvents [benzene])
• Heavy metals (arsenic, lead, and cadmium are blamed for kidney cancer and some bone cancer)
• Obesity
• Hormonal influence (prostate cancer is often androgen-dependent)
• Chronic inflammation (Crohn’s disease or ulcerative colitis and colon cancer)
• Environmental pollution (radon and lung cancer)
• Exposure to ultraviolet (UV) light and skin cancer

It is prudent to remember that we are yet to find out what exactly leads to failure in the cell division and replication that leads to cancer. Having a risk factor does not mean you will get cancer. Similarly, you may get a certain type of cancer even in absence of any risk factor.