What is Cancer?

Cancer is the name that scientists have given to a collection of related diseases that are characterized by the abnormal and continuous growth of cells.

Cancer can start almost anywhere in the human body, affecting any age group and typically presents as solid tumors (masses of tissue) with the exception of cancers of the blood.

Cancerous tumors are malignant and thus capable of spreading into and invading nearby tissues. Additionally, as these tumors grow, cancer cells may break off and travel to other regions in the body to form new tumors far from the original tumor location.

Another type of tumor are benign tumors which do not spread into or invade nearby tissues but can grow to be very large. When these tumors are removed, they do not grow back. Malignant tumors however, may grow back.

So, what causes cancer? 

  • Cancer is a genetic disease caused by changes to the genes that control the way that our cells grow and divide
  • Genetic changes that cause cancer may be inherited from one’s parents, but can also arise during a person’s lifetime.
  • Lifetime genetic changes may be cause by errors that occur as our cells divide or may occur due to DNA damage caused by certain environmental exposures
  • Environmental exposures that may lead to cancer include: tobacco smoke, exposure to the sun’s ultraviolet rays
  • It is important to note that no two cancers have the same genetic changes. Furthermore, as the cancer continues to grow, there may be additional changes that complicate the treatment of the cancer.


More than 100 different types of cancer have been identified. Cancers are typically named for the organs or tissues where they came from and may also be described by the type of cell that formed them

Common cancer types include: 

  • Breast cancer
  • Colon and rectal cancer
  • Endometrial cancer
  • Kidney cancer
  • Lung cancer
  • Pancreatic cancer
  • Non-Hodgkin lymphoma (cancer that starts in the lymphocytes)
  • Melanoma (cancer that begins in cells with melanocytes (I.e., skin cells)
  • Leukemia (cancer that begins in the blood-forming tissue of the bone marrow)


Risk factors for cancer: 

Although it’s difficult to determine why one person is more likely to develop cancer over another, research has shown that there are certain risk factors that may increase a person’s chances of developing cancer

  • Cancer risk factors include exposure to chemicals or other substances as well as certain behaviors. Other risk factors also include things that people cannot control like age and family history 
    • Factors that may affect the risk of cancer
      • Diet
        • Your diet refers to the foods that you eat on a regular basis
        • Diet is being studied as a risk factor for cancer, however this line of research is difficult because some of the foods that a person eats may actually protect against cancer. Additionally, it is difficult to track what people eat over a long period of time
        • More research still needs to be done to truly understand the link between diet and cancer development
      • Alcohol
        • Research studies have shown that drinking alcohol is linked to an increased risk of developing the following cancers:
          • Breast cancer
          • Colorectal cancer (in men)
          • Esophageal cancer
          • Oral cancer
      • Physical activity
        • Studies have shown that individuals who are physically active have a lower risk of developing certain cancers than those who are not
        • Still, more research needs to be done to understand if the physical activity itself is the reason for this difference in risk for cancer
      • Obesity
        • Research studies show that obesity is linked to a higher risk for developing the following types of cancer:
          • Postmenopausal breast cancer
          • Colorectal cancer
          • Endometrial cancer
          • Pancreatic cancer
        • Obesity affects cancer risk in the following ways:
          • Inflammation in the body
          • Cell and blood vessel growth
          • Cell’s ability to live longer than they normally would
          • Levels of certain hormones such as insulin and estrogen which can fuel cell growth
        • Despite research linking obesity to increasing individual’s risks of cancer, research on how losing weight might lower the risk of developing cancer is limited
          • However, there’s growing evidence that weight loss might reduce the risk of some types of cancer including breast cancer (after menopause) and endometrial cancer
          • Additionally, some body changes that occur as a result of weight loss seem to suggest that losing weight may reduce cancer risk as for example obese people who intentionally lose weight have reduced levels of hormones like insulin and estrogen that are related to cancer risk.
      • Diabetes
        • Some studies have shown that individuals living with diabetes are at a slightly increased risk of having the following types of cancer
          • Bladder cancer
          • Breast cancer in women
          • Oropharyngeal cancer
          • Oral cancer
          • Pancreatic cancer
        • The reason for this link is believed to be because diabetes and cancer share some of the same risk factors including:
          • Being older
          • Being obese
          • Smoking
          • Not eating a healthy diet
          • Not exercising
        • More research is still needed however to determine if the increased risk for cancer is due to a patient being diabetic or simply because of the risk factors themselves.
      • Environmental risk factors
        • Exposure to chemicals and other substances in the environment has been shown to be linked to some cancers, including:
          • Links between air pollution and cancer risk such that exposure to secondhand tobacco smoke, outdoor air pollution and asbestos is linked with developing lung cancer
          • Drinking water with large amounts of arsenic is linked to the risk for developing skin, bladder and lung cancers.
    • Factors that are known to increase the risk of cancer
      • Cigarette smoking and tobacco use
        • Tobacco use is strongly linked to an increase risk for many kinds of cancer. In fact, smoking cigarettes is the leading cause of the following types of cancer
          • Kidney cancer
          • Lung cancer
          • Oral cavity cancer
          • Pancreatic cancer
          • Stomach cancer
        • Not smoking or quitting smoking lowers an individual’s risk of getting and dying from cancer
      • Infections
        • Certain viruses and bacteria are able to cause cancer
        • However, cancers resulting from infections are more common in the developing world (~ 1 in 4 cases of cancer) than in the developed world (< 1 in 10 cases of cancer)
        • Examples of cancer-causing infections include:
          • Human papillomavirus (HPV) which increases the risk for cancers of the cervix, penis, vagina and anus
          • Hepatitis B and hepatitis C, which increase the risk for liver cancer
          • Helicobacter pylori, which increases the risk for gastric/stomach cancer
        • Fortunately, two vaccines have been developed to minimize the risk of cancer-causing infections. The first is the vaccine for Hepatitis B and the other is for HPV
      • Radiation
        • Being exposed to radiation is a known cause of cancer. There are two main types of radiation linked to an increase risk for cancer:
          • Ultraviolet radiation from sunlight
          • Ionizing radiation which includes things like medical radiation from x-rays, CT scans…etc and radon gas in homes
      • Immunosuppressive medicines after organ transplant
        • Immunosuppressive medicines are those that are used after an organ has been transplanted from one person to another
        • These medicines work to stop an organ that has been transplanted from being rejected
        • The side effect of these medications, however, is that by decreasing the body’s immune response to help keep a transplanted organ from being rejected, they increase the risk of developing cancer because the body’s defense mechanism has been lowered.


Although some of these risk factors can be avoided, some such as growing older cannot. Still, it is recommended that you limit your exposure to avoidable risk factors as this will ultimately lower your risk of developing certain cancers.

For a video summary of the risk factors for cancer, watch the following: Risk Factors for Cancer (National Cancer Institute)