Does cancer run in families?

If you have a relative with cancer, probably one of the most pressing questions is what your chances are of getting it yourself. In a paper published in PloS Medicine, the premier medical journal freely available online, Laufey Amundadottir and colleagues from deCODE genetics (a company that is using genetics to develop new drug treatments) and Iceland’s National-University Hospital go some way toward answering that question.

They analyzed comprehensive data on the most common forms of cancer from Iceland’s National Cancer Registry in the context of deCODE’s nationwide genealogy database. This enabled Dr. Amundadottir and her team to establish how often cancers occurred in first through fifth degree relatives of some 32,000 cancer patients over the past 50 years.

For 16 of the 27 cancers studied, the results indicate that relatives of patients are at a significantly higher risk of developing cancer than are members of the population at large. For some cancers this increased risk even extended out to distant (i.e. 3rd to 5th degree) relatives. Cancers in certain sites also showed a familial association with other cancers—for example relatives of individuals with stomach, colon, rectal, or endometrial cancer were more likely to develop one of these cancers, although not necessarily in the same site as did their relative. Three cancers—stomach, lung and colon cancer—were also seen more frequently in the mates of patients, confirming that shared lifestyle or environmental factors such as smoking, diet or exercise habits also contribute substantially to the increased risk.

The seven cancers with the highest increased familial occurrence both in close and distant relatives were breast, prostate, stomach, lung, colon, kidney and bladder cancers. However, even for these cancers the increased relative risk for first-degree relatives was generally less than twice that for the population at large, and this risk diminished significantly for second-degree and more distant relatives.

“By utilizing a population approach, we have been able to draw a portrait of cancer risk as a public health problem over the span of many decades. Our findings indicate that genetic factors contribute to the risk of specific cancers, but also that certain types of cancer can be looked upon collectively as broad, complex phenotypes. The next step in this work is to isolate the key genes contributing to the common forms of the disease and to use this information to develop better medicine. At the same time it is crucial to emphasize that lifestyle and environmental factors play a very significant role in the development of cancer and are things we may all be able to do something about today,” said Kari Stefansson, CEO of deCODE and senior author on the study.

Citation: Amundadottir L, Thorvaldsson S, Gudbjartsson D, Sulem P, Kristjansson, et al. (2004) Cancer as a complex phenotype: Pattern of cancer distribution within and beyond the nuclear family. PLoS Med 1 (3): e65. Full Article