To establish whether transgenic mouse models of mammary tumorigenesis are relevant models for human breast cancer in terms of their response to 5-ALA, we have evaluated three well-characterised transgenic strains that develop mammary tumours under powerful oncogenic stimulation – HRAS, PyVT and SV40 Tag – for their ability to accumulate PpIX following administration of 5-ALA. The gene discussed is HRAS; the disease is breast carcinoma.