The identification of signalling pathways that control cell progression, apoptosis or other common hallmarks of cancer are currently used to describe mechanisms and differences between individual tumours or tumour subtypes (e.g. oncogene and tumour suppressor proteins in breast cancer: Ras, c-Myc, p53; in colorectal cancer: Apc, Mlh1, Mlh2; or prostate cancer: Myc, Bcl-2, Hpn, PCA-3, P53 etc.). Here, MLH1 is linked to breast cancer.