Abstract: The present invention relates generally to the field of human genetics. Specifically, the present invention relates to methods and materials used to isolate and detect a human breast cancer predisposing gene (BRCA2), some mutant alleles of which cause susceptibility to cancer, in particular breast cancer. More specifically, the invention relates to germline mutations in the BRCA2 gene and their use in the diagnosis of predisposition to breast cancer. The present invention further relates to somatic mutations in the BRCA2 gene in human breast cancer and their use in the diagnosis and prognosis of human breast cancer. Additionally, the invention relates to somatic mutations in the BRCA2 gene in other human cancers and their use in the diagnosis and prognosis of human cancers. The invention also relates to the therapy of human cancers which have a mutation in the BRCA2 gene, including gene therapy, protein replacement therapy and protein mimetics.