By analyzing hotspot CDMs that are reported to be both common and uncommon in breast cancers, this study explored the prevalence of lower mutant frequency tumor subpopulations of prevalent breast cancer mutations (e.g., PIK3CA mutations) and determined whether mutations rarely detected in breast cancers using low-sensitivity methods (e.g., KRAS mutations) are found in breast cancers using a high-sensitivity mutation detection method. This evidence concerns the gene PIK3CA and breast cancer.