CARRIERS consortium findings
The study led by Dr. Couch was carried out by the Cancer Risk Estimates Related to Susceptibility (CARRIERS) consortium. It involved analyzing data from 17 epidemiology studies that focused on women in the general population who develop breast cancer. For the studies, which were conducted in the United States, pathogenic variants in 28 cancer-predisposition genes were sequenced from 32,247 women with breast cancer (case patients) and 32,544 unaffected women (control persons).
In the overall CARRIERS analysis, the prevalence of pathogenic variants in 12 clinically actionable genes was 5.03% among case patients and 1.63% among control persons. The prevalence was similar in non-Hispanic White women, non-Hispanic Black women, and Hispanic case patients, as well as control persons, they added. The prevalence of pathogenic variants among Asian American case patients was lower, at only 1.64%.
Among patients who had breast cancer, the most common pathogenic variants included BRCA2, which occurred in 1.29% of case patients, followed by CHEK2, at a prevalence of 1.08%, and BRCA1, at a prevalence of 0.85%.
Mutations in BRCA1 increased the risk for breast cancer more than 7.5-fold; mutations in BRCA2 increased that risk more than fivefold, the investigators stated.
Mutations in PALB2 increased the risk of breast cancer approximately fourfold, they added.
Prevalence rates for both BRCA1 and BRCA2 among breast cancer patients declined rapidly after the age of 40. The decline in other variants, including ATM, CHEK2, and PALB2, was limited with increasing age.
Indeed, mutations in all five of these genes were associated with a lifetime absolute risk for breast cancer greater than 20% by the age of 85 years among non-Hispanic Whites.
Pathogenic variants in BRCA1 or BRCA2 yielded a lifetime risk for breast cancer of approximately 50%. Mutations in PALB2 yielded a lifetime breast cancer risk of approximately 32%.
The risk of having a mutation in specific genes varied depending on the type of breast cancer. For example, mutations in BARD1, RAD51C, and RAD51D increased the risk for estrogen receptor (ER)–negative breast cancer as well as triple-negative breast cancer, the authors noted, whereas mutations in ATM, CDH1, and CHEK2 increased the risk for ER-positive breast cancer.
“These refined estimates of the prevalences of pathogenic variants among women with breast cancer in the overall population, as opposed to selected high-risk patients, may inform ongoing discussions regarding testing in patients with breast cancer,” the CARRIERS authors observed.
“The risks of breast cancer associated with pathogenic variants in the genes evaluated in the population-based CARRIERS analysis also provide important information for risk assessment and counseling of women with breast cancer who do not meet high-risk selection criteria,” they suggested.
Similar findings in second study
The second study was conducted by the Breast Cancer Association Consortium under lead author Leila Dorling, PhD, University of Cambridge (England). This group sequenced 34 susceptibility genes from 60,466 women with breast cancer and 53,461 unaffected control persons.
“Protein-truncating variants in five genes (ATM, BRCA1, BRCA2, CHEK2, and PALB2) were associated with a significant risk of breast cancer overall (P < .0001),” the BCAC members reported. “For these genes, odds ratios ranged from 2.10 to 10.57.”
The association between overall breast cancer risk and mutations in seven other genes was more modest, conferring approximately twice the risk for breast cancer overall, although that risk was threefold higher for the TP53 mutation.
For the 12 genes the consortium singled out as being associated with either a significant or a more modest risk for breast cancer, the effect size did not vary significantly between European and Asian women, the authors noted. Again, the risk for ER-positive breast cancer was over two times greater for those who had either the ATM or the CHEK2 mutation. Having mutations in BARD1, BRCA1, BRCA1, PALB2, RAD51C, and RAD51D conferred a higher risk for ER-negative disease than for ER-positive disease.
There was also an association between rare missense variants in six genes – CHEK2, ATM, TP53, BRCA1, CDH1, and RECQL – and overall breast cancer risk, with the clearest evidence being for CHEK2.
“The absolute risk estimates place protein-truncating variants in BRCA1, BRCA2, and PALB2 in the high-risk category and place protein-truncating variants in ATM, BARD1, CHEK2, RAD51CC, and RAD51D in the moderate-risk category,” Dr. Dorling and colleagues reaffirmed.
“These results may guide screening as well as prevention with risk-reducing surgery or medication, in accordance with national guidelines,” the authors suggested.
The CARRIERS study was supported by the National Institutes of Health. The study by Dr. Dorling and colleagues was supported by the European Union Horizon 2020 research and innovation programs, among others. Dr. Narod disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.