Data from the huge Swedish Family-Cancer Database indicate that families qualifying for BRCA1/2 testing have a slightly greater risk of developing cancers of several internal organs, but the clustering of ovarian cancer, early pancreatic cancer, and early onset prostate cancer in some of those families appears to be unrelated to BRCA1/2 mutations, according to researchers at the German Cancer Research Center.
“In families with some cases of breast cancer, or breast cancer together with ovarian cancer, most of these cases are not attributable to BRCA1 or 2 mutations. I guess this is the most important point of the article,” researcher Justo Lorenzo Bermejo told Pharmacogenomics Reporter.
The Swedish database contains medical information on more than 10.2 million individuals, which researchers Lorenzo Bermejo and Kari Hemminki narrowed to 944,723 families that had at least three generations of information available.
Although the study’s outcome confirms previous results, it also produced data on the risk of pancreatic, prostate and stomach cancers, said Lorenzo Bermejo. “We have observed some risks for other cancers, and the risks are higher than in the whole population, but the cumulative risk in high-risk families — for example, for stomach cancer — is only moderate,” he said.
Individuals from high-risk families who receive negative BRCA1/2 test results must still be watchful. “Even if you don’t have these mutations, you have a high cancer risk,” said Lorenzo Bermejo. “We have found that only 14 percent of the women affected by breast cancer are in high-risk families, and only 4.8 percent of the women with ovarian cancer are in families eligible for mutation testing,” he said.
Families with at least one breast- and one ovarian-cancer case have a BRCA1 mutation frequency of 43 percent, while families having at least one case of male breast cancer have a BRCA2 mutation frequency of 23 percent, according to research conducted by the German Consortium for Hereditary Breast and Ovarian Cancer. Both situations represent the greatest risk factors for inheriting the respective mutations, Lorenzo Bermejo and Hemminki wrote.
The researchers classified families that are eligible for mutation testing into groups defined by the German Consortium for Hereditary Breast Cancer: two or more breast-cancer cases before age 50; a case of male breast cancer; a breast cancer and an ovarian cancer cases; two breast cancer cases, one before age 50; two breast cancers after age 50; and one breast cancer case before age 35.
“Before testing for mutations, we only know if people have breast cancer or not — we cannot screen the whole population — we have to check, and the best possibility is to begin with those high-risk families,” Lorenzo Bermejo said.
By clarifying the contributions of BRCA1 and 2, the findings will encourage other cancer researchers to concentrate on finding and characterizing additional related genes, said Lorenzo Bermejo. “BRCA1 and BRCA2 only explain a limited proportion of breast and ovarian cancers.”