Beclin 1 is functionally a haploinsufficient tumour suppressor gene in mice and is monoallelically deleted in some sporadic breast, ovarian and prostate cancers (5,6), although its role as a haploinsufficient tumour suppressor in cancer patients has been questioned as these deletions appear to also invariably include loss of BRCA1 (42). The gene discussed is BECN1; the disease is prostate carcinoma.