Deletion of the chromosome regions containing the BRCA1 and BRCA2 genes, for example, are commonly observed in inherited ovarian cancer and breast cancer [34,35] and complete inactivation of the APC gene, a tumour suppressor gene related to a number of cancers, is caused by LOH in oesophageal and non-small cell lung cancer [36,37] and other specific cancer types [7] (chapter 7). Here, BRCA2 is linked to cancer.