If your dad, aunt, or even great-grandpa had colorectal cancer, you may need more screening for the disease than you thought.

In the largest population-based study of its kind to date, researchers from Huntsman Cancer Institute (HCI) at the University of Utah found that up to 10% of colorectal cancers may be missed when current screening guidelines are followed by people with a family history of colon polyps (called adenomas) that lead to colorectal cancer.

Family history is a known factor for increasing a person’s risk of colorectal cancer. This study showed the increased risk to first-degree relatives (parents, siblings, and children) to be as much as  80% higher than in people with no family history of precancerous polyps. The study also detected an elevated risk in more distant second- and third-degree relatives (aunts, uncles, grandparents, cousins, nieces, nephews, and 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, principal investigator of the study and an HCI physician. "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," he added.

Samadder and his team of researchers made this finding based on nearly 127,000 individuals who underwent colonoscopy in Utah between 1995 and 2009. The results appeared in the October 2013 issue of Cancer.

The study wouldn’t have been possible without resources unique to Utah. The study required data from the Utah Population Database (UPDB) along with records from Intermountain Healthcare (Intermountain) and HCI—part of the University of Utah Health Care (UUHC) system—which together provide cancer care to more than 80% of people in Utah. The UPDB contains genealogies often dating back to the early 1800s along with data from the Utah Cancer Registry, statewide inpatient discharge and ambulatory surgery records, driver license data, and birth and death certificates.

"No other study has combined genealogical and cancer data with records from two major health care organizations (Intermountain and UUHC) which have integrated electronic patient data," said Samadder.

Current guidelines recommend people with a first-degree relative diagnosed with colorectal cancer or advanced polyp (adenoma) before age 60 should undergo colonoscopy starting at age 40. Samadder says the study’s results open the discussion about screening strategies for family members of patients with adenomas.

"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 before age 60, but also for those first-degree relatives of patients diagnosed after age 60," said Samadder. "We need to continue 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."

Many patients wonder if colon cancer runs in their family if even one family member has had the disease. "The risk of colorectal cancer increases with even one affected family member, but increases substantially with multiple affected family members or an early age of cancer diagnosis," says Samadder. "Most colon cancer is sporadic, meaning it develops in people who do not have any family history of the disease. In this group, colon cancer usually does not appear until after the age of 60. But in familial colorectal cancer, the disease generally appears earlier—perhaps in a person's 40s or early 50s."

Colorectal cancer is the third most common cancer in the United States and the second deadliest. Patients concerned about their risk for the disease should talk with their doctor or with a genetic counselor, especially if family members have had colorectal cancer, to create a cancer screening plan based on the person’s individual and familial risk. Learn more about familial cancer risk from HCI’s Family Cancer Assessment Clinic.