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Colorectal cancer risk is increased in first-degree relatives
Clinical Question
What is the risk of colorectal cancer in family members of patients with colorectal cancer?
Bottom line
People with a first-degree relative (parent, sibling, or half sibling) with colorectal cancer (CRC) or with 2 second-degree relatives with CRC are at increased likelihood of developing CRC over their lifetime as compared with the general population (6% vs 4%). Having 2 or more siblings or a parent and sibling with CRC increases the risk to 9%. 1b
Reference
Study design: Cohort (prospective)
Funding: Government
Setting: Population-based
Synopsis
These authors used the Nationwide Swedish Cancer registry to identify 173,796 people born after 1958 who developed CRC, and crossed-referenced these patients with their first-degree and second-degree relatives using a multigeneration registry that connects people with their relatives, linking a total of more than 16 million people. By looking at a patient's parents they could calculate that patient's risk and by linking to his or her siblings they could look for the sibling's risk. These databases keep track of everyone who lived in Sweden over an average 33.6 years of follow-up. Over their lifetime, a person with either one first-degree relative (parent or sibling) or 2 second-degree relatives (grandparent, aunt, or uncle) with CRC has a risk of approximately 6% (1 in 17), a 60% increase in likelihood compared with people without a first-degree relative with CRC. A similarly increased risk was seen in half siblings (6%; 95% CI 1.3 - 1.8). People with both a parent and sibling or half sibling with CRC had a 3.6-fold increase in cumulative incidence (9%). Having only one second-degree relative with CRC showed a minor association with the risk of CRC.
Reviewer
Allen F. Shaughnessy, PharmD, MMedEd
Professor of Family Medicine
Tufts University
Boston, MA
Comments
6% vs 4%
This is one of those studies where the relative risk scares you to death, and the absolute risk difference is actually a bit reassuring. Well, if not reassuring then at least not as terrifying.