The present invention relates to a genetically modified pig as a model for studying breast cancer, mitochondria related protein folding disorders and/or epidermolysis bullosa simplex. The modified pig model displays one or more phenotypes associated with any of said disorders. Disclosed is also a modified pig comprising a modified endogeneous BRCA1 and/or BRCA 2 gene, and/or a modified ornithine transcarbamylase gene, and/or a modified Keratin 14 gene and/or a transcriptional or translational product or part thereof. The invention further relates to methods for producing the modified pig; and methods for evaluating the effect of a therapeutical treatment of breast cancer, mitochondria related protein folding disorders and/or epidermolysis bullosa simplex; methods for screening the efficacy of a pharmaceutical composition; and a method for treatment of a human being suffering from breast cancer, mitochondria related protein folding disorders and/or epidermolysis bullosa simplex are disclosed.