Of note, the signatures related to the APOBEC3B enzyme (signatures 2 and 13) contributed to 58.8% of the mutations of the HR+/HER2− metastatic tumors as compared to only 31.9% in the primary TCGA samples (p < 2e-16), confirming previous work demonstrating a link between APOBEC-mediated mutagenesis and the acquisition of subclonal mutations [26]. The gene discussed is APOBEC3B; the disease is metastatic neoplasm.