The aims of this study were (i) to characterise the 19q12 amplicon in breast cancer, (ii) to determine the genes that are overexpressed when amplified in this amplicon, (iii) to investigate which of the genes mapping to this amplicon are selectively required for the survival of cells harbouring their amplification, and (iv) to determine if cancer cells with CCNE1 gene amplification are dependent on CCNE1 cell cycle-related functions for their survival. The gene discussed is CCNE1; the disease is breast cancer.