December 4, 2004

A deCODE study just published in Public Library of Science (PloS) Medicine provides the most comprehensive analyses to date of the importance of inherited risk factors for the most common forms of cancer. The results indicate that increased risk of different types of cancers can be caused by the same genetic variability.

The study brings together two population-based datasets: the Icelandic Cancer Registry’s information on all cancers diagnosed in Iceland over the past fifty years, and deCODE’s nationwide genealogy database, which made it possible to look well beyond the nuclear family, thereby minimizing the effect of common environmental factors on the results. By analyzing the familial relationships of 32,000 cancer patients over half a century, the authors were able to examine how cancer runs in families as a common disease. This generated a detailed portrait of the familal risk of cancer and showed that relatives of cancer patients are at an increased risk of developing cancer, even beyond the nuclear family and at other sites than their relatives. The article, entitled “Cancer as a complex phenotype: Pattern of cancer distribution within and beyond the nuclear family,” is available at www.plos.org.

For most of the 27 cancers studied, the study shows that first-degree relatives of patients are at approximately twice the risk of developing cancer than are members of the population at large. For many cancers a lesser but still statistically significantly increased risk extends beyond the nuclear family, even to fifth-degree relatives. One of the most significant findings is that cancers in certain sites also showed a familial association with other cancers — for example relatives of individuals with colon cancer are at an increased risk not only for cancer of the colon, but also for cancers of the rectum, prostate and stomach. Three cancers, stomach, lung and colon cancer, were also seen more frequently in the mates of patients, confirming that shared lifestyle or environmental factors also contribute substantially to the increased risk.

These findings suggest that the identification of the genes involved in cancer predisposition may enable the development of better means of treatment, and of developing diagnostic tests to identify those who are at higher risk and thereby maximize the effectiveness of prevention strategies.