Colorectal cancer in the family: Are earlier screening tests worth it?

The answer to the first question was relatively clear. The researchers found a total of seven studies that looked into whether the relatives of people with colorectal cancer are also more likely to develop colorectal cancer.

These studies suggest that people under the age of 55 are two to four times more likely to develop colorectal cancer if they have a close blood relative who has had colorectal cancer. This is only true for first-degree relatives, though – in other words, mainly parents, sisters or brothers. But it's not clear whether the increased risk is due to an inherited genetic predisposition, similar lifestyles, or a combination of both.

The risk of colorectal cancer is very low in young people, but it increases with age. So colorectal cancer screening tests are offered to people aged 50 and over in Germany: Statutory health insurers cover the costs of one test for blood in stool (poo) per year in men and women between the ages of 50 and 54. If you are aged 50 or over (men) or 55 or over (women), you can decide to have a colonoscopy instead.

The risk is generally higher in people whose families have a history of colorectal cancer, though. So it could be a good idea to offer them colonoscopies earlier. But colonoscopies can have disadvantages, too. The researchers at IQWiG specifically looked for studies on the benefits and harms of colorectal cancer screening in younger people with colorectal cancer in their family.

The results here are disappointing. Although there are studies that looked at the benefits and harms of the occult blood test and sigmoidoscopy (endoscopic examination of the lower part of the colon), they focused on older people and didn't take family risk factors into account. The IQWiG researchers found only two studies that looked into colonoscopies in people who had a family-related risk: The results of one of these studies couldn't be used. The other study had various flaws and didn't distinguish between younger and older people who had a family-related risk.

So it's not clear whether there are more overall advantages or disadvantages to doing colorectal cancer screening tests in people under the age of 55 with close relatives who have (had) colorectal cancer.

Some experts suggest that doctors should routinely ask their patients whether any of their close relatives have had colorectal cancer. But there's no guarantee that this question will be answered correctly because many people are embarrassed to talk about problems affecting that part of their body. Research has shown that people who have colorectal cancer often don't talk about it with their family. This means that people might unintentionally give a wrong answer to the seemingly simple question, “Have any of your close relatives had colorectal cancer?”

So the researchers at IQWiG also tried to find out how reliable the answers to questions like that are. Their findings here were also sobering. Although there are questionnaires for this purpose, it's not clear how reliable the answers are. The IQWiG researchers didn't find any research on written questionnaires.

Worldwide, they only found one U.S. study and one Swedish study on interviews. In both studies, the participants were first asked about illnesses in the family. Then their answers were checked, for instance by looking at their relatives’ medical records. Some of the people who took part in the studies were a lot older than 55. The studies show that many people don't really know whether their family members have had colorectal cancer:

• In one of the studies, 47 out of 100 people who had a relative with colorectal cancer didn't know about it, compared to 19 out of 100 people in the other study. The wrong answers led to doctors missing a family-related genetic predisposition (a "false negative” result). These people wouldn't have access to special screening offers.
• Wrong answers were also given by people who didn't have a family-related predisposition: 6 out of 100 people in the studies said they had a relative with colorectal cancer, although that wasn't the case. They possibly confused colorectal cancer with another medical condition. So if their answers weren't checked, these people would be wrongly classified as having a higher risk of colorectal cancer (a "false positive" result). If they were offered special screening health care services, they wouldn't benefit from them.

These studies also show that a seemingly simple question can have negative effects too: Someone who believes that their risk of cancer is higher based on the answer that they've given may already start worrying because of it. And not knowing about an existing risk can be a problem too: If you have a false sense of security, you might not make use of possibly important colorectal cancer screening offers.