Age, Chronic Illness, and Life Expectancy after a Diagnosis of Colorectal Cancer

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The summary below is from the full report titled "The Effect of Age and Chronic Illness on Life Expectancy after a Diagnosis of Colorectal Cancer: Implications for Screening." It is in the 7 November 2006 issue of Annals of Internal Medicine (volume 145, pages 646-653). The authors are C.P. Gross, G.J. McAvay, H.M. Krumholz, A.D. Paltiel, D. Bhasin, and M.E. Tinetti.

What is the problem and what is known about it so far?

Screening is looking for a specific condition in people who do not report symptoms of that condition. Doctors screen patients for cancer so that cancer may be found while it is still small and has not spread. Treatment at this early stage offers a better chance of a cure. However, for several years after starting screening, the cancer death rate in screened patients is often similar to that of unscreened patients. This is because the increased survival from screening is due to detection and treatment of early-stage cancer—cancer that would not have resulted in death for at least 5 years if it had not been detected by screening. As a result, patients with a life expectancy of less than 5 years when screening detects a small cancer are unlikely to extend their lives by screening. For instance, testing for blood in the stool to screen for cancer of the colon or rectum (colorectal cancer) reduces the cancer death rate only after about 4 years of screening. If patients die of other diseases, such as heart disease, during the time when screening doesn't alter the cancer death rate, screening hasn't done them much good. When a person's age and disease burden make it likely that they will die before screening reduces the cancer death rate, screening probably isn't worthwhile.

Why did the researchers do this particular study?

To determine what situations shorten people's lives to the point where screening for colorectal cancer is unlikely to help them to live longer.

Who was studied?

Patients with colorectal cancer who were included in a database sponsored by the National Institutes of Health that combines data from the Surveillance, Epidemiology, and End Results (SEER) Program and data from Medicare.

How was the study done?

The authors studied information about each patient's colorectal cancer, age, and chronic diseases (such as diabetes, heart disease, and lung disease) when colorectal cancer was diagnosed. Using this information, they calculated the average length of life after diagnosis for people of different ages and with different chronic diseases at the time of cancer diagnosis.

What did the researchers find?

People who were older and had more chronic diseases had a shorter average length of life after cancer diagnosis. Men and women older than 75 years of age who had 3 or more chronic diseases lived 5 years or less, even after an early diagnosis of colorectal cancer. In contrast, people older than 75 years of age with no chronic diseases lived 10 to 16 years, on average, after early diagnosis of colorectal cancer.

What are the limitations of the study?

The authors did not count chronic diseases that developed after the cancer diagnosis. Also, the rates of chronic diseases were probably higher than those measured.

What are the implications of the study?

Older people with several chronic diseases have a lower chance that colorectal cancer screening will help them live longer. If the person is older than 75 years of age and has 3 or more chronic diseases, screening for colorectal cancer may not be worthwhile. Older people with no chronic diseases are more likely to live long enough to benefit from screening.