Is cancer caused by risky behavior or bad luck?


I thought cancer was the result of risky behaviors like smoking and spending too much time in the sun. But then I read an article about cancer and bad luck. So which is it — behaviors or luck?


I know the article you are referring to, and I wasn’t very happy with the way it was presented by the media. Let me start with the bottom line: Cancer is caused by (1) our genes, and by (2) our lifestyle (risky behaviors) and environment. It’s not just one or the other.

Sometimes genes that we inherit from our parents cause cancer. An example is the BRCA1 gene that causes some cases of breast cancer.

Many cancer-causing genetic changes, however, occur after we are born. Sometimes, risky behaviors produce changes in our genes. An example is how cigarette smoke affects certain genes in the lungs and other organs to cause cancer.

Factors in the environment that may or may not be influenced by our behavior can cause cancer. Examples are cancers of the uterus (cervix), liver and stomach caused by various viruses and bacteria. Or skin cancers as the result of unprotected exposure to sunlight.

The study you refer to involved a complex analysis of cancers and stem cells in multiple different organs. Each of our organs has its own stem cells. Organ stem cells are there to replace older cells in the organ when those older cells die. Stem cells divide frequently.

The study was asking whether some cancers occur simply because an organ’s stem cells divide frequently. That could cause cancer because each time a cell divides, there is a risk of developing genetic changes (“bad luck”). If so, organs that have the most frequently dividing stem cells might have the greatest risk of cancer.

That’s what the researchers found. And they estimated that about two-thirds of all cancers might result from such bad luck.

In my opinion, the authors’ conclusion that bad luck accounts for most cancers is questionable on two grounds. First, we know that the rates of some cancers (like skin cancer, or nose and throat cancer) are a hundred times more common in some parts of the world than others. That implies a huge effect of the environment.

Second, using the phrase “bad luck” implies that there is nothing to be done about random cancer-causing genetic changes. That may be true currently, but it is entirely possible that a deeper understanding of the biology of cancer will reveal ways to reduce the risk of such random changes.

I think it’s unwise to say that most cancer is caused by bad luck — particularly when the argument is quite speculative. That’s because it could discourage us from pursuing a healthy lifestyle, and from getting cancer screening tests that can catch cancers at a curable stage. (I’ve put a table of recommended cancer screening tests below.)

We can control our fate, though not completely. That’s true of minimizing our risk of cancer, as well. Cancer is not just a matter of bad luck.

 Prevention guidelines

Guidelines and screening technology are always evolving, with new recommendations from medical organizations and societies. Which test is best, and how often to be tested, may vary depending on the technology used and your risk for particular illnesses. Discuss this with your doctor.

Test or exam Recommendation
Breast cancer
Breast self-exam There’s not enough evidence to prove that this is a valuable screening tool. However, monthly exams give women the opportunity to note and report lumps or other suspicious changes in a breast, and many doctors recommend monthly self-exams because they are simple to do. If you choose to do self-exams, have a clinician show you the correct technique.
Breast exam by clinician Annually after age 40. (Women in their 20s and 30s should have one every three years, at least.)
Mammogram Every two years for women ages 40 and older, though more frequent screening may be indicated for those at higher risk of breast cancer. Some professional societies recommend an annual mammogram and breast MRI (see next entry) for those at moderate or high risk. Talk with your doctor about the best age at which to stop routine screening.
Breast MRI If you are at moderately increased risk for breast cancer (a 15% to 20% lifetime risk), the American Cancer Society (ACS) suggests discussing risks and benefits of having breast MRI plus a mammogram annually. Women at moderate risk include those with

  • a history of breast cancer, DCIS, LCIS, or atypical cell changes
  • breasts that are extremely dense or unevenly dense on mammograms.
  • If you are at high risk for breast cancer (a lifetime risk greater than 20%), the ACS recommends having a breast MRI and a mammogram annually. Women at high risk include those with
  • a known BRCA gene mutation, or a close relative (parent, sibling, child) known to have this
  • past radiation therapy to the chest between ages 10 and 30
  • a condition that raises breast cancer risk or a close relative who has such a condition, such as Li-Fraumeni syndrome or Cowden syndrome.
Cervical cancer
Pelvic exam and Pap test (conventional or liquid-based) Every year (conventional Pap test) or every two years (liquid-based Pap test) starting at age 21 or about three years after the onset of sexual intercourse (whichever is first). Starting at 30, the ACS recommends screening every two to three years for women who have had three or more consecutive normal Pap tests. (Another option for these women is having a conventional or liquid-based Pap test plus the human papilloma virus test every three years.) Women over 70 who have had three consecutive normal Pap tests and no abnormal Pap results for 10 years may elect to stop screening. You may need more frequent screening if your doctor determines your risk for cervical cancer is high.
Colorectal cancer
Fecal occult blood test (gFOBT), sigmoidoscopy, or colonoscopy The U.S. Preventive Services Task Force (USPSTF) recommends screening for colorectal cancer using fecal occult blood testing, sigmoidoscopy, or colonoscopy in adults, beginning at 50 and continuing until 75. The risks and benefits of these screening methods vary, so ask your doctor which is best for you and how often to repeat the test. The USPSTF recommends against routine screening for people ages 76 to 85, unless you and your doctor determine that there are special circumstances to support such testing. Testing is not recommended for adults over 85.
Lung cancer
Lung CT scan While lung cancer kills more men and women annually than any other type of cancer, yearly CT screening is recommended only for high-risk adults ages 55 to 79. High-risk adults in this age group include those who have smoked a pack a day for 30 years (or some equivalent amount, such as two packs a day for 15 years) and who are still smoking or who have quit within the past 15 years. The USPSTF does not recommend screening for “casual” smokers.
Prostate cancer
Prostate-specific antigen (PSA) test Experts disagree. Some recommend a PSA test annually at age 50, or age 45 if you are at high risk for prostate cancer (have a father, brother, or son diagnosed with prostate cancer before 65 or are African American), or at age 40 if you are at very high risk (have several close relatives who were diagnosed before 65). Others don’t believe there is sufficient evidence to recommend PSA tests and endorse its use only for surveillance after a diagnosis of prostate cancer or to monitor treatment of the disease.
Rectal exam Experts disagree. Some say this is not of proven value as a screening test for prostate cancer. However, the exam sometimes detects rectal cancer or blood in the stool originating from another disease. Therefore, it may be worthwhile as a routine screening; talk to your doctor about the age to begin having this exam and how often to repeat it.
Skin cancer
Skin exam Regular self-exam to note any suspicious changes, and periodic yearly exam by your doctor at check-ups.
If you’re at high risk, particularly for melanoma, a specialist should do the exam. See the doctor if you have a mole that’s 6 millimeters or larger in diameter, is asymmetrical, and has irregular borders and a mixture of colors.