MSH6 and rectal cancer: This individual (9033) had a microsatellite unstable caecal cancer which failed to express the mismatch repair protein MLH1 by immunohistochemistry, as well as a rectal cancer that was microsatellite stable and expressed the mismatch repair proteins MLH1, MSH2 and MSH6. The microsatellite unstable caecal cancer did not display the typical pathological features of a sporadic MSI colorectal cancer, in that it was nonmucinous, of low histological grade and BRAF mutation negative (data not shown).