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Breast Cancer Genes Tied to Other Malignancies

But risk of pancreatic, prostate, stomach cancer still low, study finds

MONDAY, Nov. 15, 2004 (HealthDayNews) -- Data on nearly a million families suggest that mutations in BRCA1 and BRCA2 genes -- which are strongly linked to some breast cancers -- may also confer a slight increase in risk for pancreatic, prostate and stomach cancers.

However, that increase poses little real threat to those who carry either one of these gene mutations, experts added.

"Even though there's an association, I think they should be reassured that, while the risk for breast or ovarian cancer is fairly high, the risk for these other cancers is still pretty low," said Debbie Saslow, director of breast and gynecologic cancers at the American Cancer Society.

About 10 years ago, researchers identified mutations in BRCA1 and BRCA2 -- two large, unrelated genes -- that boost the risk for breast and ovarian cancer.

According to Saslow, up to 8 percent of all breast cancers may be attributed to mutations in one of these two genes, although not all carriers will develop the disease.

Still, women from families with a strong history of breast or ovarian cancer may want to consider genetic testing and counseling, she said. According to Saslow, "strong family history" doesn't mean an isolated case of breast cancer, even when that cancer occurs at a relatively young age.

"With strong family history, we're talking two or more relatives, especially at a young age, or the occurrence of rarer cancers -- ovarian cancer is much rarer than breast cancer in women, as is male breast cancer," she explained. "Also, when a woman develops cancer in one breast and then, later on, in the second breast. Bilateral breast cancer is much rarer than cancer in just the one breast."

Women mulling over genetic testing may also wonder if the BRCA1 and BRCA2 genes predispose them to other cancers.

To help settle that question, researchers led by Dr. Lorenzo Bermejo, of the German Cancer Research Center in Heidelberg, examined data from the Swedish family-cancer database, one of the largest such databases ever compiled.

Analyzing information on genetics and cancer incidence from nearly 948,000 Swedish families collected over three generations, the researchers found that individuals with mutations in BRCA1 and BRCA2 were at a somewhat increased risk for malignancies of the pancreas, prostate and stomach, compared to non-carriers.

For example, members of BRCA-affected families with a history of both breast and ovarian cancer were nearly twice as likely to develop stomach cancer compared to members of the general population. However, in terms of the overall incidence of stomach cancer, "that risk is still tiny," Saslow said, meaning that the actual incidence of these cancers remained very low.

"It's like asking, 'What's twice the risk of getting hit by lightning?'" Saslow said. "It's still a very rare event."

The study, published in the November issue of the Annals of Oncology, did confirm BRCA1's and BRCA2's links to breast and ovarian cancer. But the Swedish data also suggest the two cancers are not always linked: In families hit by one case of breast cancer and one case of ovarian cancer, most of the ovarian cancers were not caused by BRCA1 or BRCA2, the researchers found. In those cases, ovarian cancers appear to have arisen separately, due to undetermined genetic or environmental factors.

The study provides important information on who should be most concerned about their genetic risks, Saslow said. But she cautioned that genetic testing may not be for everyone.

"An important question would be, 'What would I do with that information once I got it?' Let's say you had three sisters with breast cancer, but you know you're not going to do anything differently if you find out you have this gene," Saslow said. "Then testing might not be worth it."

"On the hand, if your family has a history of breast cancer and you worry every day 'I might get breast cancer,' then finding out you don't have the gene might help," she added. "Or you might decide to have prophylactic [breast-removing] surgery. Then, you'd definitely want to get tested beforehand, of course, because who wants to get that surgery if they don't need it?"

Discussing these issues with a doctor beforehand is important, Saslow said.

More information

To learn more about genes and other breast cancer risk factors, visit the American Cancer Society.

SOURCES: Debbie Saslow, Ph.D., director, breast and gynecologic cancer, America Cancer Society; Atlanta; November 2004 Annals of Oncology
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