Many recent advances in single‐cell sequencing technologies build on this earlier work, providing the ability to examine the subclonal architecture and evolutionary dynamics of human cancers at a significantly enhanced resolution (Figure 2). For example, WGS of single tumour cells in two triple‐negative (ER‐, PR‐, HER2‐) breast cancers revealed the existence of distinct, highly aneuploid, subclonal tumour cell populations that shared partially related but divergent copy number profiles [37]. The gene discussed is ERBB2; the disease is breast cancer.