Second, the heterogeneity of HER2 copy number status in DCIS can be explained by their phylogenetic relationship where DCIS ducts with HER2 amplification evolve from surrounding ducts that lack HER2 amplification, and this evolutionary progression during the acquisition of HER2 amplification in DCIS involves multiple genomic changes. The gene discussed is ERBB2; the disease is ductal breast carcinoma in situ.