Genetic Testing in Older Women with Breast Cancer

SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. Approximately 284,200 new cases of breast cancer will be diagnosed in 2021 and about 44,130 individuals will die of the disease, largely due to metastatic recurrence.

Genetic testing for cancer susceptibility with multigene testing panels is now becoming widely available and affordable. Identification of Pathogenic Variants in predisposition genes such as BRCA1 and BRCA2 among carriers has provided benefit through early intervention. There are 12 established breast cancer predisposition genes implicated among breast cancer cases, unselected for family history or young age at breast cancer diagnosis. Only loss-of-function through protein truncation and missense variants labeled as pathogenic, are classified as Pathogenic Variants-PV in the ClinVar database. They include ATM, BARD1, BRCA1, BRCA2, CDH1, CHEK2, NF1, PALB2, PTEN, RAD51C, RAD51D, and TP53. Among these genes, BRCA1, BRCA2, and PALB2 are high risk genes, whereas the other genes are considered moderate risk. Identifying high risk genes in women with breast cancer is relevant both for prevention and treatment. Breast cancer prevention opportunities include contralateral prophylactic mastectomy or surveillance with MRI of the breast, prophylactic salpingo-oophorectomy for BRCA mutation carriers, avoidance of radiation in TP53 mutation carriers, and genetic testing for family members. PARP inhibitor LYNPARZA® (Olaparib) is indicated for the treatment of patients with deleterious or suspected deleterious germline BRCA1/2 mutated, HER2-negative metastatic breast cancer who have been treated with chemotherapy in the neoadjuvant, adjuvant or metastatic setting. Younger age at diagnosis, strong family history of breast and/or ovarian cancer, Ashkenazi Jewish ancestry, or Triple Negative Breast Cancer (TNBC), are all associated with hereditary breast cancer and approximately 10% of these patients carry a Pathogenic Variant in a breast cancer predisposition gene.

According to the NCCN guidelines, hereditary cancer testing for women with breast cancer diagnosed at age greater than 65 years, without specific risk factors such as Ashkenazi Jewish ancestry or family history of cancer, has limited clinical utility as these women have less than 2.5% chance of having a Pathogenic Variant in a high risk gene. However, few studies have specifically evaluated breast cancer predisposition genes in women over age 65 years.

The authors conducted this study to determine the prevalence of Pathogenic Variants in established breast cancer predisposition genes, and to estimate remaining lifetime risks of breast cancer associated with Pathogenic Variants, among women over age 65 years in the general population. A total of 26,707 women over age 65 years from population-based studies (N=13,762, 51.5% with breast cancer and N=12,945, 48.5% age and study matched unaffected women controls) were tested for Pathogenic Variants in germline breast cancer predisposition gene. The researchers then assessed the frequencies of Pathogenic Variants and associations between Pathogenic Variants in each gene and breast cancer, and estimated the remaining lifetime breast cancer risks for non-Hispanic White women with Pathogenic Variants.

The researchers noted that the frequency of Pathogenic Variants in established breast cancer predisposition genes were identified in 3.18% of 13,762 women with breast cancer and 1.48% of the 12,945 age-matched unaffected controls. Pathogenic Variants in the high risk BRCA1, BRCA2, and PALB2 genes were found in 3.42% of women diagnosed with ER-negative breast cancer and 3.01% of women with Triple Negative Breast Cancer. The frequency of Pathogenic Variants in the high risk genes was low among women with no first degree relatives with breast cancer and ER-positive breast cancer. Pathogenic Variants in BRCA1, BRCA2, PALB2 and CHEK2 were associated with increased risks (Odds Ratio=2.9-4.0) of breast cancer. The remaining lifetime risk of breast cancer from age 66 to 85 years was more than 15% or more for those with Pathogenic Variants in BRCA1, BRCA2, and PALB2.

The authors concluded that based on this largest study to date of population-based US women over age 65 years, diagnosed with breast cancer, all women diagnosed with Triple Negative Breast Cancer or ER-negative breast cancer should receive genetic testing and that women over age 65 years with BRCA1 and BRCA2 Pathogenic Variants and perhaps with PALB2 and CHEK2 Pathogenic Variants should be considered for breast MRI screening, as they continue to be at an increased risk of breast cancer.

Risk of Late-Onset Breast Cancer in Genetically Predisposed Women. Boddicker NJ, Hu C, Weitzel JN, et al. J Clin Oncol 2021;39:3430-3440.