From a prospective feasibility study in patients affected by breast cancer and in women with a known mutation in BRCA1 or BRCA2, we report for the first time the in vivo feasibility of autofluorescence to detect (white light occult) breast cancer precursor lesions by autofluorescence ductoscopy, confirmed by histology of the subsequently performed mastectomy. Here, BRCA1 is linked to breast carcinoma.