Non-BRCA1/2 Breast Cancer Susceptibility Genes: A New Frontier with Clinical Consequences for Plastic Surgeons

Implementation of Risk-Stratified Breast Cancer Prevention With a Polygenic Risk Score Test in Clinical Practice

Background

Breast cancer (BC) screening with mammography reduces mortality but considers currently only age as a risk factor. Personalized risk-based screening has been proposed as a more efficient alternative. For that, risk prediction tools are necessary. Genome-wide association studies have identified numerous genetic variants (single-nucleotide polymorphisms [SNPs]) associated with BC. The effects of SNPs are combined into a polygenic risk score (PRS) as a risk prediction tool.

Objectives

We aimed to develop a clinical-grade PRS test suitable for BC risk-stratified screening with clinical recommendations and implementation in clinical practice.

Design and methods

In the first phase of our study, we gathered previously published PRS models for predicting BC risk from the literature and validated them using the Estonian Biobank and UK Biobank data sets. We selected the best performing model based on prevalent data and independently validated it in both incident data sets. We then conducted absolute risk simulations, developed risk-based recommendations, and implemented the PRS test in clinical practice. In the second phase, we carried out a retrospective analysis of the PRS test's performance results in clinical practice.

Results

The best performing PRS included 2803 SNPs. The C-index of the Cox regression model associating BC status with PRS was 0.656 (SE = 0.05) with a hazard ratio of 1.66. The PRS can stratify individuals with more than a 3-fold risk increase. A total of 2637 BC PRS tests have been performed for women between the ages 30 and 83. Results in clinical use overlap well with expected PRS performance with 5.7% of women with more than 2-fold and 1.4% with more than 3-fold higher risk than the population average.

Conclusion

The PRS test separates different BC risk levels and is feasible to implement in clinical practice.

Evidence for accelerated aging in mammary epithelia of women carrying germline BRCA1 or BRCA2 mutations

During aging in the human mammary gland, luminal epithelial cells lose lineage fidelity by expressing markers normally expressed in myoepithelial cells. We hypothesize that loss of lineage fidelity is a general manifestation of epithelia that are susceptible to cancer initiation. In the present study, we show that histologically normal breast tissue from younger women who are susceptible to breast cancer, as a result of harboring a germline mutation in BRCA1, BRCA2 or PALB2 genes, exhibits hallmarks of accelerated aging. These include proportionately increased luminal epithelial cells that acquired myoepithelial markers, decreased proportions of myoepithelial cells and a basal differentiation bias or failure of differentiation of cKit+ progenitors. High-risk luminal and myoepithelial cells are transcriptionally enriched for genes of the opposite lineage, inflammatory- and cancer-related pathways. We have identified breast-aging hallmarks that reflect a convergent biology of cancer susceptibility, regardless of the specific underlying genetic or age-dependent risk or the associated breast cancer subtype.

Factors that impact risk management decisions among women with pathogenic variants in moderate penetrance genes associated with hereditary breast cancer

There is limited information known about how women with pathogenic variants (PV) in moderate penetrance genes make decisions to manage their increased risk of breast cancer. This study analyzed factors that may impact decision-making surrounding management for increased breast cancer risk. Women with a PV in a moderate penetrance gene associated with increased risk for breast cancer were identified from an institutional database. Semi-structured, qualitative interviews were conducted to analyze decision-making factors. Themes were developed using deductive codes based on previous literature and inductive codes based on interviewee responses. The 16 participants (mean age = 55.9 years) included 12 women with a breast cancer diagnosis. Six women (37.5%) chose bilateral mastectomy (BM), and 10 women (62.5%) chose surveillance as management. Of the 12 women with a personal history of breast cancer, four chose to have BM (33.3%). Two women without a personal history of breast cancer chose to have BM (50.0%). Transcriptions revealed seven comprehensive themes, as well as themes unique to affected and unaffected women (Cohen's kappa = 0.80). Physician opinion was the only factor present in all interviews reported to influence risk management decision-making. Several themes were consistent with prior BRCA1/BRCA2 research (family history, risk perception, sibling influence, and physician opinions). Autonomy and insurance/finances were also important factors to participants. There were certain differences in decision-making factors between affected and unaffected women, such as partner influence. Results indicate an opportunity for providers to engage their patients in a decision-making process.