A family history of cancer raises your overall risk of developing cancer, including types of cancer far removed from those suffered by your relatives, according to a new study of 23 000 people.
Doctors have long known that people have an increased risk of developing the same type of cancer as a close relative. In addition, some genetics studies have found that common gene mutations can increase the risk of different types of cancer, for example, one genetic abnormality can increase risk of both breast and ovarian cancer in women.
But this review, performed by European researchers and published July 25 in the journal Annals of Oncology, found that a close family member's history of cancer appears to increase a person's risk of suffering either the same cancer or a different type of cancer.
"It looks like there clearly are associations between family members developing cancer and you developing cancer," said Dr Dennis Kraus, director of the Center for Head and Neck Oncology at the New York Head & Neck Institute at Lenox Hill Hospital in New York City. He was not involved with the new research.
"It's a well-done study," Kraus said. "It's a huge number of patients where they had controls, and they were able to take into account lifestyle and try to remove things like smoking and drinking from the equation."
Significant associations found in the study include:
- A 1.5-fold increased risk of breast cancer in women with a history of colorectal cancer in the family.
- A 3.3-fold increased risk of oral and pharyngeal cancer among people who had a first-degree relative with cancer of the larynx (voice box).
- A four-fold increased risk of cancer of the esophagus among people with a first-degree relative who had oral or pharyngeal cancer.
- A 2.3-fold increased risk of ovarian cancer among those with a first-degree relative who had breast cancer.
- A 3.4-fold increased risk of prostate cancer if a first-degree relative had bladder cancer.
First-degree relatives are parents, brothers, sisters, sons and daughters.
"Our results point to several potential cancer syndromes that appear among close relatives and that indicate the presence of genetic factors influencing multiple cancer sites," said study co-author Dr Eva Negri.
"These findings may help researchers and clinicians to focus on the identification of additional genetic causes of selected cancers and on optimising screening and diagnosis, particularly in people with a family history of cancer at a young age," said Negri, head of the laboratory of epidemiologic methods at the Mario Negri Institute for Pharmacological Research in Milan, Italy.
The researchers from Italy, Switzerland and France looked at 12 000 cases of cancer occurring in 13 different parts of the body between 1991 and 2009, and matched them to control cases of 11 000 people without cancer. For both groups they collected information on any cancer in the family, as well as data on health and lifestyle factors that can influence a person's cancer risk.
"A major strength of our study is that we were able to adjust our analyses for tobacco, alcohol and a number of other lifestyle habits, which most previous studies have not been able to do," Negri said.
The study's reliance on survey data, however, is a significant weakness that may have caused the authors to overstate the odds of cancer risk, said Mia Gaudet, director of genetic epidemiology for the American Cancer Society.
"At the time the cases are reporting family history, they already know they have cancer," Gaudet said. "It's an emotional time, and they are more likely to recall family members who have had cancer."
Follow-up genetic research
By the same token, the comparison patients without cancer may be less likely to recall family instances of cancer because they don't have the same motivation. "This can really introduce differences in how individuals recall any particular exposures, and this difference could be particularly profound when it comes to cancer," Gaudet said.
Follow-up genetic research into the potential associations between different types of cancer reported by the European researchers is warranted, she said.
In addition, people with a family history of cancer might want to discuss with their physician whether they should see a genetic counselor to assess their cancer risk, Gaudet said.
This emphasis on genetics, however, should not discourage people with a family history of cancer, both Kraus and Gaudet said.
"We can't control where we get our genes, but what you can control is your risk factors," Kraus said, noting that healthy diet, an active lifestyle and avoiding drinking or smoking can play just as important a role as genetics in determining a person's cancer risk.
Although the study found a link between higher risk for different types of cancer in people whose close family members had cancer, it did not establish a cause-and-effect relationship.
To learn more about genetics and cancer, visit the American Cancer Society.