What are the causes of cancer?

There are an estimated 18.1 million new cancer cases globally, and cancer remains the second-leading cause of death in the United States, where more than 1.7 million people are diagnosed with cancer every year. Cancer is often discussed as if it’s one thing. But while unrestrained growth is the common denominator, cancer can develop in a variety of different ways, due to a variety of different factors. Some we inherit, and others we are exposed to throughout our lives. It can be categorized into hundreds of different diseases based on the cells in which it arises. And when each patient’s genetic background is taken into account, no two cases are identical.

To save more lives from cancer, therefore, it will be necessary to address this complexity. Through basic research into cancer biology and immunology, we can improve our understanding of how cancer develops and how it interacts with the immune system. In this way, it could enable us to discover new, more effective ways to treat cancer.

When does cancer occur?

Cellular Definition of Cancer

Cancer begins when cells acquire the ability to grow uncontrollably and ultimately invade and damage the body’s normal tissues. Cancer development happens in multiple stages, from precancerous changes to malignant tumors. However, not all cancers form tumors, and different cancers can develop at different rates. Sometimes cancer cells spread from their original site to other places in the body through the bloodstream or lymphatic system—a process called metastasis.

Where does cancer occur?

Cancer’s Point of Origin

Cancer can affect many different parts of the body, from the skin, bone, blood vessels, and muscle, to the lungs, kidneys, and many other organs. Cancer can also affect the immune system, which plays a key role during both the development and progression of cancer.

Can you inherit cancer?

Genetic Causes of Cancers

Genes are segments of DNA located on chromosomes, and can mutate over time to become cancerous. These mutations can result from a variety of causes, including diet and lifestyle choices as well as exposure to certain environmental factors. Overall, only 5 to 10 percent of all cancers are genetically inherited, although these are the cancers that tend to occur earlier in life.

One such inheritable genetic disorder that is associated with increased cancer risk is Lynch syndrome, which prevents cells’ ability to repair their DNA when damage occurs. This can lead to cancers of the colon and uterus at an early age. Another such genetic factor is the BRCA family of genes, certain forms of which have been linked to breast and ovarian cancer.

Today, scientists and clinicians are using and developing new tests to search for biomarkers, which can help determine risks and appropriate treatment options based on an individual patient’s genetic profile.

Does behavior or lifestyle cause cancer?

Behavioral Causes of Cancer

There are a number of behavioral factors that can lead to genetic mutations and, as a result, lead to the development of cancer.

• Tobacco
• Tanning (excessive exposure to ultraviolet light)
• Diet (red, processed meats)
• Alcohol
• Unsafe sex (leading to viral infection)
• Inflammatory conditions, such as ulcerative colitis or obesity

An example of a behavioral risk factor is smoking, which can lead to lung cancer, or excessive exposure to the sun’s ultraviolet (UV) rays, which can cause skin cancer. Some dietary choices, including red meat and alcohol, have also been linked to certain types of cancer, while obesity is associated with higher rates of cancer as well, a link that CRI investigators Harvard Medical School’s Lydia Lynch, PhD, and University of California, San Diego’s Zhenyu Zhong, PhD, are independently exploring further. One’s diet can also affect the bacteria that reside within our intestines, known as the gut microbiome, and recent research by scientists, such as Johns Hopkins University’s Cynthia Sears, MD, have revealed that certain bacteria can impact the likelihood of colorectal cancer development as well as patient responsiveness to treatment with immunotherapy.

Can where you live or work cause cancer?

Environmental Causes of Cancer

Exposure to certain factors in the environment, such as chemicals like asbestos and benzene, as well as talcum powder and various sources of radiation (including excessive X-rays), can also cause cancer. These substances capable of damaging DNA and triggering cancer are referred to as carcinogens.

• Excessive sun exposure (UV)
• Chemical carcinogen exposure
• High-dose chemotherapy and radiation (mainly in children being treated for existing cancers)
• Hormonal drugs
• Immune-suppressing drugs (taken by transplant recipients)
• Radioactive materials, e.g., radon

In addition to other factors associated with aging and senescence, older individuals are more likely to have had exposure to environmental risk factors and are therefore diagnosed with cancer much more frequently than young people. When it comes to children with cancer, new immunotherapy approaches are providing for the possiblity of treating them not only more effectively, but also without some of the damaging side effects that can accompany conventional treatments.

Do viruses or bacteria cause cancer?

Viral and Bacterial Causes of Cancer

Theories surrounding bacterial causes of cancer date back over 100 years, put forth by the Father of Cancer Immunotherapy, Dr. William B. Coley. A person’s behavior and surroundings can expose them to bacteria and viruses known to cause cancer.

• Human papillomavirus (HPV)
• Hepatitis B (HBV) and hepatitis C (HCV) viruses
• Epstein–Barr virus (EBV)
• Human T-lymphotropic virus
• Kaposi's sarcoma-associated herpesvirus (KSHV)
• Merkel cell polyomavirus
• Helicobacter pylori

Exposure to the B and C strains of the hepatitis virus can result in liver cancer, and sexual transmission of certain strains of the human papillomavirus (HPV) can result in cervical cancer, anal and penile cancers, and several head and neck cancers.

A vaccine that protects against hepatitis B virus has been available since 1982; in fact, this vaccine was the first preventive cancer vaccine in existence. The Cancer Research Institute funds research into both preventive and therapeutic cancer vaccines, including Dr. Ian Frazer’s groundbreaking work on the development of Gardasil, the first preventive vaccine against cervical cancer.

Bacteria and viruses can also be engineered to fight cancer on our behalf. Oncolytic virus therapy uses modified viruses to infect tumor cells and cause them to produce chemicals that signal danger to the immune system before self-destructing. Antibodies that target cancer antigens can be engineered through a process called phage display, in which a bacteriophage (a virus that infects bacteria) can be used to evolve new proteins.

Although there are number of elements at play in the development of cancer, the treatments at our disposal are constsntly improving and adapting as new research provides insight into various risk factors. Learn more about why immunotherapy research matters and how CRI’s innovative approach has shaped the progress of cancer treatments. You can contribute to continued breakthroughs in cancer research and treatment options by making a donation to CRI today.