When current national screening guidelines are followed for people with a family history of adenomas (colon polyps that lead to colon cancer), up to 10 percent of colorectal cancers could be missed.
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 made this finding based on nearly 127,000 individuals who underwent colonoscopy in Utah between 1995 and 2009. The results appear online in "Early View" of the journal Cancer
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 percent higher than in relatives of patients without these conditions. The study also detected smaller percentages of elevated risk in more distant second- (aunts and uncles, grandparents) and third-degree relatives (cousins, nieces and nephews, great-grandparents).
"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 N. Jewel Samadder, MD, MSc, principal investigator of the study and an HCI investigator. "The biggest surprise was the percentage of missed cancers under the current guidelines. We figured there would be a few percent, but 10 percent is a large number," he added.
For the general population, current national colon cancer screening guidelines recommend colonoscopy every 10 years starting at age 50. For first-degree relatives of people diagnosed with colorectal cancer or advanced adenomas before they were 60 years old, increased screening is recommended—colonoscopies every five years starting at age 40. The screening recommendations for more distant relatives of people diagnosed before 60 and for all relatives of people diagnosed at or after age 60 are the same as for the general public.
"Our results support the current screening guidelines, but they also raise the issue of whether some level of more aggressive screening should be considered, not only for first-degree relatives of patients with polyps diagnosed at or below age 60, but also for those first-degree relatives of patients diagnosed above age 60.," said Samadder. "To validate other components of the current screening guidelines, we need to continue with a more in-depth examination of the risk of colorectal cancer in relatives of patients diagnosed with colorectal cancer or advanced adenomas, looking at factors such as the size of the polyp, the degree of cell abnormality and location of the tumor in the bowel."
The study examined colonoscopy results from Utah residents between 50 and 80 years of age, linking them with cancer and pedigree information from the Utah Population Database (UPDB). "The records came from both Intermountain Healthcare and University of Utah Health Care, which represents 85 percent of all patient care in Utah and includes facilities from academic medical centers to small rural clinics," said Samadder. "No other study has combined genealogical and cancer data with records from two major health care organizations which have integrated electronic patient data."