Comparative Genomic Profiling of Second Breast Cancers following First Ipsilateral Hormone Receptor–Positive Breast Cancers

Patient-matched FBC and SBC analysis revealed that only a minority of patients exhibited common gene variants between the first and second tumor. Further analysis using larger cohorts, preferably using single-cell analyses to account for clonality, might better select patients with true recurrences and thereby better inform the decision-making process.