While larger studies, such as the new Confluence project (https://dceg.cancer.gov/research/cancer-types/breast-cancer/confluence-project), may lead to improved statistical power to detect CNV associations, evaluating uncommon genetic variation such as CNVs that overlap SULT1A1 and other potential modifier genes in BRCA1/2 pathogenic variant carriers will remain a challenge. The gene discussed is BRCA1; the disease is breast cancer.