• the primary endpoint is the identification of cases with evidence of loss of the product of one of the four main MMR genes on tumour histology.
  

• Secondary outcome measure is the survival and response to treatment of the identified cases.
  

All patients at the Royal Marsden with a diagnosis of colorectal cancer will be eligible to enter this study. This will include patients both with early and advanced disease, provided they give informed consent. They will give written consent to participate, to include consent for analysis of existing tumour tissue and consent for collection of demographic and clinicopathological data relating to their case and its future outcome, and consent for a blood sample to be taken for research purposes. Additionally, old samples of material surplus to clinical requirements may be collected without specific consent if there is no possibility that it would affect the patient's interest (eg the patient has died).