ERBB2 and neoplasm: Key oncogenes such as MYC, MYCN, EGFR, PDGFRA, MET, HER2, DHFR, CDK4 and MDM2 have been frequently observed on ecDNAs, suggesting that ecDNA‐mediated oncogene amplification is an important driver of tumour development and progression (Decarvalho et al, 2018; Gu et al, 2020).