Family History Studies of Colorectal Cancer Flawed

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(ChemotherapyAdvisor) – Research that links family history of adenomatous polyps to increased risk for colorectal cancer (CRC) is flawed, a systematic review funded by the National Cancer Institute published in the May 15 issue of Annals of Internal Medicine has found.

“…we have determined that most studies purporting to show that a family history of adenomas is a risk factor for CRC are not designed to test this hypothesis,” wrote Thomas F. Imperiale, MD, of Indiana University Medical Center, Indianapolis, IN, and David F. Ransohoff, MD, of the University of Chapel Hill, Chapel Hill, NC. “Rather, they assess whether persons with adenomas are more likely to have a family history of CRC.”

They found that sparse, better-designed studies “suggest that the risk for CRC may be increased when a first-degree relative has 1 or more adenomas, but these studies have methodological problems that limit both the validity and the generalizability of their results.”

The study authors performed a sequential review of titles, abstracts, and text from articles retrieved from MEDLINE and Cochrane databases from 1966 through 2011 and identified 10 studies used to answer the question, “Does having a first-degree relative with an adenoma increase the risk for CRC?”

Instead, they determined these studies answered the question, “Does having a first-degree relative with CRC increase the risk for an adenoma?” This is an important distinction, they noted, as the data influence guidelines determining when CRC screening should begin.

Two additional studies were found that provided more relevant information. One study showed risk for CRC in persons who have first-degree relatives with adenomas to be 2.31%, greater than the risk in persons who do not have first-degree relatives with adenomas, 0.53% (RR, 4.36). The second study found those with first-degree relatives with large adenomas had a risk of 8.3% for CRC or adenomas ≥1cm, compared with a 4.2% risk in persons whose first-degree relatives did not have adenomas or CRC, (adjusted OR, 2.27).

“Further studies are needed that examine subgroups of adenomas (advanced, nonadvanced) and identify factors that modify the risk for CRC,” they concluded.


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