Familial Link for Colorectal Cancer Detected in Half-Siblings

A study published in The BMJ found that a family history of colorectal cancer (CRC) is similarly associated with a risk for half-siblings as it is for siblings.

Researchers used the Nationwide Swedish Family Cancer Database that includes all people residing in Sweden and born after 1931 with their biological parents (from 1958-2015), for a total of more than 16 million individuals. Among those with clear genealogy records, 173,796 people developed CRC.

Sibling and half-sibling risk

The overall lifetime cumulative risk of CRC in siblings of patients was 7%, which represents a 1.7-fold (95% CI, 1.6-1.7; n=2,089) increase over the risk in those without any family history of CRC. A similarly increased lifetime cumulative risk of 6% was observed among half-siblings (standardized incidence ratio [SIR] = 1.5; 95% CI, 1.3-1.8; n=140), representing a 1.5-fold increased risk.

Familial risk assessment

The risk for individuals with CRC in both a parent and a half-sibling (SIR=3.6; 95% CI, 2.4-5.0; n=32) was similar to the risk associated with those with both an affected parent and an affected sibling (SIR=2.7; 95% CI, 2.4-3.0; n=396). “We showed that family history of CRC in a half sibling (with no other affected first/second-degree relative) has a much stronger association with increased risk of CRC than such a family history in other second-degree relatives,” senior study author Mahdi Fallah, MD, PhD, of the German Cancer Research Center and the National Center for Tumor Diseases in Heidelberg, told Reuters.

“These evidence-based findings provide novel information to help to identify people at high risk with a family history of CRC that can potentially be used for risk adapted screening,” the researchers concluded.