What are Risks for Cancer?

What are Risks for Cancer?

This article describes risk factors for common cancers. It will be discussed how common symptom interpretation can be guided by risk factor assessment.

A risk factor for a particular cancer implies that they are often found in association. For example, one of the most well-known cancer risk factors is cigarette smoking. It is estimated that tobacco is the single largest cause of cancer in the United States. A common misconception is that risk factors or associations mean that it “causes” the cancer. While there are many chemicals in tobacco that likely do contribute to the formation of a cancer, it is far too simplistic to say they cause the cancer. For example, if you consider 100 people who have smoked 2 packs a day for twenty years – what percentage of these will get lung cancer? The facts are that among heavy smokers up to 10-20% will develop lung cancer even with very similar smoking histories. This means that there are other factors that contribute to getting lung cancer (or any cancer for that matter) however it also means that not smoking greatly decreases the risk of getting lung cancer

What are the risk factors for common cancers? For common cancers, the best established risk factors and associations are:

  • Smoking – multiple sites; associated with lung, head and neck, pancreas cancers
  • Overweight – many different types of cancer
  • Sedentary lifestyle – colon and breast cancer
  • Aflatoxin – liver cancer
  • Alcohol – multiple sites; especially head and neck, esophagus, liver
  • Excessive sun exposure – skin cancer
  • Radiation exposure – leukemia, thyroid, breast, lung and bone cancers
  • Infections such as:
    • Parasite schistosomahaematobium – bladder cancer
    • HPV – human papilloma virus – cancer of the cervix, anus, rectum, mouth, throat and penis
    • Liver flukes – liver cancer
    • Bacteria H.Pylori – stomach cancer
    • HIV – multiple cancers particularly lymphoma
    • Epstein-Barr virus – lymphoma
    • Hepatitis C – liver cancer
  • Medications such as:
    • Tamoxifen – increases endometrial cancer (but decreases breast cancer)
    • Cyclosporine – lymphoma
  • Occupational hazards such as:
    • Coal dust – lung cancer, kidney cancer
    • Soot – scrotal cancer, lung cancer
    • Asbestos – lung cancers, chest cancer (mesothelioma)

Cancer risk is not just about your lifestyle or occupation, but also where you live and your ethnicity (i.e. genetics) plays a big role as well. In different areas of the world, some cancers are much more common than they are in the United States. For example:

  • Esophageal Cancer – China, East Africa
  • Stomach Cancer – Japan
  • Ovarian Cancer – Iceland
  • Liver Cancer – Thailand

Gender also plays a key role in the risk for several cancers. Women tend to have a higher frequency of thyroid, gallbladder and breast cancer. Men have a much higher rate of lung and pancreatic cancer.

How can knowledge of risk factors affect symptom evaluation? The most obvious use for risk factors assessment is to be aware of potentially harmful substances or practices and avoid them. Some risk factors are modifiable (such as cigarette smoking or diet), but some are not modifiable (such as gender or ethnicity). The importance of knowing about risk factors is that it helps create an index of suspicion for interpreting different symptoms that might suggest cancer.

For example, a nagging cough is something that most people deal with from time to time. Cough can be a sign of lung cancer. Cough is not very specific for lung cancer because there are at least a hundred causes of cough that do not involve cancer. The vast majority of coughs are not due to cancer. What if a cough develops and does not go away? Should it be ignored?

If someone were to consider if whether a man with a cough has lung cancer the best way to do this would be to determine the likelihood of it by getting more information about the cough and by understanding if any risk factors for lung cancer are present. In this way, a physician must think like a detective and not jump to any conclusions. Similarly, it would be important that a person with a nagging cough and several risk factors for lung cancer not ignore the cough as this may be a sign of lung cancer.

Duration and severity of a symptom can give insight into how important it truly is. If the cough has been present for 3 days versus 3 months, obviously the man with 3 months of coughing deserves a more closer inspection. If a cough is associated with blood in the mucus versus a dry cough, the bloody cough (also known as hemoptysis) is more concerning for cancer. A 35 year old man with a nagging cough of 1 week who has been otherwise healthy and never smoker is not as suspicious as a 50 year old man with a nagging cough of 3 months duration who has smoked for 30 years. If the 50 year old smoker with a bloody cough also says he lost 15 pounds in the past month without trying (i.e. unintentional weight loss) is now very concerning for lung cancer and needs urgent investigation.

In this way, risk factors can modify the importance of symptoms. Another example might be a healthy 30 year old woman with a breast lump. It is very unusual for a young woman to get breast cancer however if this woman said her mother and sister both had breast cancer before the age of 40 then knowledge of this risk factor (i.e. strong family history of breast cancer) would modify how this symptom would be investigated. The woman would get a biopsy in preference of repeat x-rays or ultrasound.

REFERENCES:

  1. Goldman, L ; Schafer A.I. (2011). Goldman: Goldman’s Cecil Medicine, 24th ed. Chapter 183. New York, NY: Elsevier Saunders.
  2. understandingrisk.cancer.gov/
  3. This article was originally published on September 3, 2012 and last revision and update was 9/4/2015.