Risk Can Extend to Fifth Degree Relatives

The comprehensiveness of both datasets made it possible to look well beyond the nuclear family, minimizing the effect of shared environmental factors on the results.

By analyzing the familial relationships of some 32,000 cancer patients over half a century, the authors were able to examine how cancer as a common disease and public health problem -- not solely its rarer and more strictly genetic subtypes -- runs in families. This generated a detailed portrait of the role of genetic factors in predisposition not only to particular types of cancer but to broad groups of cancers as well.

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 significant increased risk extends beyond the nuclear family and out to even fifth-degree relatives.

Shared Lifestyle Factors May Contribute to Risk

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.