For people with a family history of adenomas (colon polyps that lead to colon cancer), up to 10% of colorectal cancers could be missed when current national screening guidelines are followed. Colorectal cancer is the third most common cancer in the United States and the second deadliest.

In the largest population-based study to date, researchers from Huntsman Cancer Institute (HCI) at the University of Utah in Salt Lake City made this finding based on nearly 127,000 people who underwent colonoscopy in Utah between 1995 and 2009. The results were published in Cancer (2013; doi:10.1002/cncr.28227).

Family history of colon cancer is widely accepted as a factor that increases risk for the disease. This study quantified the increased risk to first-degree relatives (parents, siblings, children) of patients with adenomas or advanced adenomas at 35% to 70% higher than in relatives of patients without these conditions. The study also detected smaller percentages of elevated risk in more distant second- (grandparents, aunts, uncles) and third-degree relatives (cousins, nieces, nephews, great-grandparents).

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“We expected to see increased risk in first-degree relatives, but we weren’t sure the risk would also be higher for more distant relatives in multiple generations,” said principal investigator N. Jewel Samadder, MD, MSc, of HCI. “The biggest surprise was the percentage of missed cancers under the current guidelines. We figured there would be a few percent, but 10% is a large number.”

For the general population, current national colon cancer screening guidelines recommend colonoscopy every 10 years starting at age 50 years. For first-degree relatives of people with a colorectal cancer diagnosis or advanced adenomas before they were 60 years old, increased screening is recommended—colonoscopies every 5 years starting at age 40 years. The screening recommendations for more distant relatives of people younger than 60 years at diagnosis and for all relatives of people 60 years and older at diagnosis are the same as for the general public.

“Our results support the current screening guidelines,” said Samadder. The results also raise the issue of whether more aggressive screening should be considered for first-degree relatives of patients with polyps diagnosed at 60 years or younger, as well as for those first-degree relatives of patients older than 60 years at diagnosis. She explained that the current screening guidelines can be validated by a more in-depth examination of the risk of colorectal cancer in relatives of patients with colorectal cancer or advanced adenomas.

The study examined colonoscopy results from Utah residents age 50 to 80 years, linking them with cancer and pedigree information from the Utah Population Database. Samadder explained that the records came from both Intermountain Healthcare and University of Utah Health Care, which represents 85% of all patient care in Utah and includes facilities from academic medical centers to small rural clinics. This is the only study to combine genealogical and cancer data with records from two major health care organizations that have integrated electronic patient data.