The research, in this week's Lancet, assessed cancer rates among the relatives of patients with inflammatory bowel disease (IBD).
From this they determined whether an association between the two diseases exists.
The population-based study identified 114,102 first-degree relatives by registry linkage. Each subject was followed up for cancer occurrence. Standardized incidence ratio (SIR) of cancer was used as relative risk.
560 colorectal cancers were identified among the relatives.
The group found that first-degree relatives of patients with Crohn's disease or ulcerative colitis were not at increased risk of cancer. The relative risk was 0·96 for colon cancer and 0·78 for rectal cancer.
|First-degree relatives of Crohn's disease or ulcerative colitis patients did not have an increased cancer risk
The SIRs were not affected by age, relation to patient, or type or extent of IBD in the patient.
Relatives of patients with both IBD and colorectal cancer had an 80% increased risk of colorectal cancer, found Dr Johan Askling, from the Karolinska Institute in Stockholm, and colleagues.
Askling said on behalf of the researchers, "Our results do not endorse a common cause of IBD and colorectal cancer.
"The slightly decreased relative risk for colorectal cancer among relatives could indicate the proportion of all colorectal cancer cases attributable to IBD."