Our findings suggest a new model (Figure 7F) for carcinogenesis in individuals who carry germline mutations truncating a single copy of BRCA2. Exposure to aldehydes like formaldehyde or acetaldehyde, which are both widespread in our environment and also accumulate endogenously in certain tissues, could potentiate spontaneous mutagenesis in the cells of mutation carriers, predisposing to cancer. The gene discussed is BRCA2; the disease is cancer.