Postmenopausal breast cancer and the benefit of genetic testing

By Dr. Ananya Mandal, MDMar 10 2020

A new study shows that genetic mutations could be detected in one in 40 women diagnosed with breast cancer before the age of 65 years. The study from Stanford researchers, titled "Prevalence of Pathogenic Variants in Cancer Susceptibility Genes Among Women With Postmenopausal Breast Cancer," was published as a research letter 10^th March in the journal JAMA.

What the study was about?

The team explained that several genetic mutations, such as BRCA1 and BRCA2, are associated with breast cancers. Detection of these genetic variants could help the first-degree female relatives of cancer afflicted persons to be aware of their risk and go for preventive management or testing etc. This study attempted to see if there was a benefit of genetic testing for these pathogenic variants of the genes in women who are diagnosed with cancer early.

Prevalence of Pathogenic Variants in Cancer Susceptibility Genes Among Women With Postmenopausal Breast Cancer. Image Credit: Yeexin Richelle / Shutterstock

At present genetic testing is performed for women with certain features such as young age at which the diagnosis was made and the history of breast and other cancers among first-degree relatives. The team of researchers explains that at present, the minimum prevalence of pathogenic variants at 2.5 percent to 10 percent decides the recommendations regarding testing the women. There are, however, no guidelines that suggest which women need to be tested. There are no guidelines regarding screening postmenopausal women who have no family history of breast cancers they wrote. The team thus compared the prevalence of these genetic variants or mutations of BRCA1, BRCA2, and BRCA1/2 among postmenopausal women with or without breast cancer.

Allison Kurian, MD, MSc, associate professor of medicine and of epidemiology and population health at Stanford, lead author of the study said, "There's been a lot of controversy in the field as to whether every woman with breast cancer should receive genetic testing in part because we didn't know how prevalent cancer-associated mutations are in this largest subgroup of newly diagnosed people -- that is, women who develop breast cancer after menopause without the presence of any known hereditary risk factors." She and Marcia Stefanick, Ph.D., professor of medicine and obstetrics and gynecology at Stanford, along with other colleagues, worked on this study.

What was done?

The research was part of the Women's Health Initiative (WHI) study that has enrolled 161 808 postmenopausal women aged between 50 and 79 years. The women were enrolled from 40 different sites across the country between 1993 and 1998.

This was a case-control study where women who had no history of breast cancer at the start were taken, and some of these developed invasive breast cancer (considered as cases) while others did not develop cancer (control participants) on 20^th September 2017. The cases were compared with the controls in terms of their genetic variants.

To test the genetic variants, Myriad Genetics used a panel of 28 different genetic variants, including "BRCA1/2, ATM, BARD1, CDH1, CHEK2, NBN, PALB2, STK11, and TP53". Associations of these genes with breast cancer were noted. These genetic variants were classified as either pathogenic, non-pathogenic, or those of "uncertain significance," benign or likely to be benign. Association with the age of the participants was also checked.

What was found?

A total of 4,517 women were included in the study for comparison. Of these, the median age at diagnosis was 73 and 81 years for cases (total 2,195 women) and controls (total 2,322 women), respectively. There were 66.3 percent and 84.9 percent whites among cases and controls, respectively. Pathological variants were seen among 148 and 93 participants among cases and controls, respectively. The association of pathological variants in any of the breast cancer-causing genes was 3.55 percent among the cases. This was 1.29 percent among the controls, and this difference was statistically significant. Testing guidelines were satisfied by 30.8 percent cases, and 20 percent of the controls found the researchers among women with BRCA1/2 variants. For testing, the team followed the National Comprehensive Cancer Network 2019 testing guidelines. These guidelines were met for other genes among 34 percent cases and 16 percent controls. When less than 65 years, the association between BRCA1/2 pathological variants was 2.21 percent and 1.09 percent among those aged over 65 years.

"Now we know that the prevalence of cancer-associated BRCA1 and BRCA2 mutations in women diagnosed with breast cancer after menopause rivals that in women of Ashkenazi Jewish descent -- a population that is currently encouraged to discuss genetic testing with their doctors," said Kurian.

What was the inference from the study?

The team wrote that this study revealed, "3.55% of unselected, postmenopausal patients with breast cancer carried PVs in breast cancer-associated genes, a 3-fold higher prevalence than among cancer-free control participants and without decrease by age." They concluded that this study shows that among postmenopausal women with breast cancer there may be a high prevalence of pathological variants, and thus testing is necessary even if there is no early diagnosis or family history of breast cancer. Kurian said. "We finally have a read on the likely benefit of testing this most common subgroup of breast cancer patients."