How to Decode Cancer Statistics
Trying to make sense of cancer statistics can be overwhelming. Adding to the confusion, many media reports lack context, and even reputable journals can promote misleading and overblown claims about cancer treatment. Understanding statistics, however, can help you evaluate treatment options and assess the reliability of the information you obtain.
When you learn you have cancer, you want to know what your chances are for a cure and how long you can expect to live. Survival rates give you a general idea about prognosis for people who have the same disease as you, but they don't tell you your chances for a cure or remission and they don't consider extenuating circumstances that may affect your outcomes.
Progression-free survival rate describes the length of time during and after treatment in which patients live with a disease that does not get worse. Disease-free survival rate is the percent of people who experience complete remission after finishing treatment.
The 5-year survival rate is probably the most common cancer statistic. It describes the percent of people in a study or treatment who are still alive five years after diagnosis or treatment for a disease, regardless if they still have the disease. For example, of 100 people who have bladder cancer, 80 were living five years after diagnosis. Scientists and oncologists often tout 5-year survival rates as evidence of success of treatment.
However, while 5-year survival rates are a valid measure for comparing cancer therapies in randomized trials, they can be misleading for describing how well cancer patients fare. Physicians are diagnosing cancers earlier and earlier, so they're finding more and more cases of cancer. They're also diagnosing benign cancers that never would have progressed (or progressed too slowly to cause problems). Both can make the 5-year survival rate look better than it actually is and does not consider patients' quality of life.
The statistic cancer patients should be most interested in is mortality rate: the number of deaths with cancer as an underlying cause occurring in a specific population in a year.
We would expect mortality rates to decline with improvements in cancer control, but according to H. Gilbert Welch, MD, author of Should I Be Tested for Cancer?, screening has not reduced mortality and in fact, in some instances, mortality rates have increased.
"Mortality rates for thyroid, prostate, and breast cancers have hardly budged since 1973, yet 5-year statistics have skyrocketed," he said in an interview. "Since 1950, the 5-year survival rate for prostate cancer has risen from 40 to 98 percent, yet the death rate remained stable."
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Evans, Imogen, Thornton, Hazel, Chalmers, Iain, and Glasziou, Paul. "Testing Treatments." Web.
National Cancer Institute. "Glossary of Statistical Terms." Web. 8 December 2009.
Mayo Clinic. "Cancer survival rate: What it means for your prognosis." Web. 6 April 2011. http://www.mayoclinic.com/health/cancer/CA00049
Welch, H. Gilbert, Schwartz, Lisa M., and Woloshin, Steven. "Are increasing 5-year survival rates evidence of success against cancer?" JAMA 283(22) 2000: 2975-2978. Web.
National Cancer Institute. "Cancer Mortality Rate." Web. 4 December 2009.
Cancer.net. "Understanding Statistics Used to Guide Prognosis and Evaluate Treatment." Web. 27 July 2011. http://www.cancer.net/patient/All+About+Cancer/Newly+Diagnosed/Understanding+Survival+Statistics
Lowe, Rachel Myers. "Cancer Screening Questioned." Cancerpage.com. Web. 14 December 2005.
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