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Study Shows Breast Cancer Risk Among BRCA Gene Carriers is High (dateline January 24, 2004)

A new study finds that women who carry a mutated form of the BRCA1 or BRCA2 gene are at significantly higher risk of developing breast cancer, compared to other women. Mutations of these genes account for only 5% to 10% of breast cancer cases. Therefore, while the number of affected women remains relatively small, the study found that young women (under age 50) with the mutated genes face an even higher risk of breast cancer, compared to previous generations of women who carry these genetic abnormalities. Women who know they carry mutated BRCA1 or BRCA2 genes are encouraged to receive regular breast cancer screening exams and talk to their physicians about preventive options, such as the drug tamoxifen or, in some cases, mastectomy.

BRCA1 (breast cancer gene 1) and BRCA2 (breast cancer gene 2) are two genes that, when functioning normally, help repair damage to DNA—a process that also prevents tumor development. In 1994, researchers discovered that women who carry mutations of BRCA1 or BRCA2 are at higher risk of developing both breast and ovarian cancer than women who do not have these genetic mutations. Mutations of these genes are uncommon, playing a role in less than 10% of breast cancer diagnoses.

In a study reported in the October 24, 2003 issue of Science, Dr. Mary-Claire King, a geneticist at the University of Washington, and her colleagues studied 104 women who carried a mutated BRCA1 or BRCA2 gene, along with over 800 of their relatives. Ninety percent of the women in the study were Ashkenazi Jews, a population shown to be a high risk of carrying BRCA gene mutations.

Dr. King and her team found that by age 80, women with BRCA gene mutations have an 82% risk of developing breast cancer, compared with a 13% risk among women without the gene mutations. Alarmingly, the study also showed that women under age 50 who were born after 1940 had a 67% risk of developing breast cancer. This is compared to a 24% risk among women carrying the BRCA gene mutations who were born before 1940. Researchers are unsure why younger women with BRCA gene mutations appear to be at even greater risk of developing breast cancer compared to previous generations with these abnormal genes.

The risk of ovarian cancer is also significantly higher among women with BRCA1 or BRCA2 gene mutations. Dr. King’s study found that women with BRCA1 gene mutations had a 54% risk of ovarian cancer and women with BRCA2 gene mutations had a 23% risk of ovarian cancer. This is compared to an average risk of 2% among other women.

Genetic testing is available to women with strong family histories of breast cancer or other risk factors. These tests can determine whether a woman is carrying BRCA gene mutations. Women who test positive for the BRCA gene mutations sometimes opt to have their breasts removed as a preventive measure, a procedure called prophylactic mastectomy. This surgery has been shown to reduce the risk of breast cancer by 90% since most all of the breast tissue is removed. Other preventive options for women at high risk of breast cancer include taking the drug tamoxifen (brand name, Nolvadex) for a period of five years, being closely monitored by physicians with mammography and/or other imaging tests, and in some cases, having the ovaries removed (prophylactic oophorectomy).

Candidates for BRCA testing include women with:

  • Breast cancer in two or more close relatives, such as a mother and two sisters
  • Early onset of breast cancer in family members, often before age 50
  • History of breast cancer in more than one generation
  • Cancer in both breasts in one or more family members
  • Frequent occurrence of ovarian cancer
  • One or more BRCA positive relatives
  • Eastern and Central European (Ashkenazi) Jewish ancestry, with a family history of breast and/or ovarian cancer (researchers have identified two types of BRCA1 mutations and one BRCA2 mutation that are especially prominent in this group)

Women at high risk of breast cancer should talk to their physicians about the advantages and disadvantages of genetic testing, and should receive regular breast cancer screening exams.

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