African-American female doctor taking white male patient's blood pressure

A person's ability to accurately remember his or her own family history of cancer is important when doctors are looking for disease that may be inherited.

The family history provided may affect how often a person is screened for a disease. Wrong information could lead to too much or too little screening.

Inherited defects in genes — those passed on from parents to children — account for about 5% to 10% of patients with colorectal cancer. This number may seem small, but colorectal cancer is the second leading cause of cancer death in the US.

One of these gene defects is called hereditary nonpolyposis colorectal cancer (HNPCC). People who carry the HNPCC flaw are more likely to get colorectal cancer at a young age. Women with this problem are at higher risk for endometrial cancer.

While genetic testing is used to look for HNPCC, usually families are identified through a family history. To help determine whether a person has HNPCC experts ask whether:

• He or she has at least three relatives with colorectal cancer
  
• The colorectal cancer involved two successive generations
  
• At least one relative had their cancer when they were younger than 50
  
• At least two of the people are first-degree relatives (mother, father, brother, or sister)

Because of their increased risk, members of families where HNPCC is present are asked to get a screening colonoscopy every one to two years starting at age 21. This recommendation is more intensive than that for colorectal screening in the general public.

But how reliable are family histories as given by patients? Reporting their results in the British Journal of Surgery (Vol. 88, No. 9: 1228-1233), researcher Niels Katballe and colleagues from Aarhus University in Denmark found they weren’t as dependable as hoped.

The doctors asked 1,200 patients who had just been diagnosed with colorectal cancer to complete a family history questionnaire. Based on the patients’ answers, 14 cases had the characteristics for HNPCC.

Because all Danish citizens are treated in a public health care system, the doctors were able to check patient responses against actual records.

When the doctors checked the health records, they found that three out of the 14 (21%) cases actually did not meet the criteria for HNPCC.

And, they found seven cases of HNPCC that would not have been discovered had they depended on the families' recollection.

The authors concluded, "The present study suggests that family studied on HNPCC are not reliable unless the diagnoses of family members are verified from official sources." The Danish doctors' access to official family health records allowed for increased understanding of health histories, and thus helped complete the needed profile for screening decisions.

The Danish study focused on only one inherited disease, but there are many others. Experts say that, in the US where family health histories may not be as easily found, the bottom line is for people to understand what diseases run in their families and keep written records, and not rely on memory. This is the key to providing accurate information when a doctor needs it.