If your cousin has cancer, you may also be at risk for the disease. That’s according to a new study that suggests the family-associated increased risk of some cancers may extend well beyond the immediate family.

Researchers found that for 16 of the 27 cancers studied, first-degree relatives of cancer patients were at significantly higher risk of developing cancer than the general population. First-degree relatives include siblings and children.

But for at least eight of the cancers, distant third- to fifth-degree relatives, such as a cousin or great-grandparent, also shared a significantly higher risk of developing the same disease.

In addition, researchers found that the mates or spouses of people with some types of cancer also had a much higher risk of developing cancer, which suggests that shared environment as well as genetics plays a major role in determining cancer risk.

Cancer Runs in Families

To look at the role family plays in influencing cancer risk for a variety of cancers, researchers analyzed all cancer cases diagnosed in Iceland from 1955 to 2002 and linked it to a genealogical database of all living Icelanders and most of their ancestors since the settlement of Iceland.

The results appear in the December issue of PLOS Medicine.

The study showed that the seven cancers with the highest incidence within both close and distant relatives were:

—Breast cancer

—Prostate cancer

—Stomach cancer

—Lung cancer

—Colon cancer

—Kidney cancer

—Bladder cancer

But researchers say even for these cancers, the increased 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.

The cancers most closely associated within families were breast, lung, kidney, pancreatic, ovarian, and esophageal cancer and multiple myeloma. First-degree relatives of people with these types of cancer had between a 2- and 3-fold risk of developing the same cancer.

The study also showed that relatives of people with stomach, colon, rectal or endometrial cancer were more likely to develop one of these cancers, although not necessarily in the same site as their relative.

In addition, researchers found that mates of people with stomach, lung, and colon cancer were more likely to develop these cancers, which suggests the role of environmental factors such as smoking, diet, and exercise in affecting cancer risk.

"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,” says researcher Kari Stefansson, of deCODE Genetics in Reykjavik, Iceland, in a news release.

“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,” says Stefansson. “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."

By Jennifer Warner, reviewed byBrunilda Nazario, MD

SOURCES: Amundadottir, L. PLOS Medicine, December 2004; vol 1. News release, Public Library of Science.