Malpractice in breast cancer can be seen as false-negative or false-positive findings which may result in either late or incorrect therapies. Biopsy material can be unintentionally interchanged, leading to incorrect treatment, and psychological damage to the patient. There is an obvious need for individualization of the tissue samples in such cases. In this study we used a multidisciplinary approach to integrate DNA technology that has been standardized and used in forensic science for other purposes, mainly to prove malpractice that has been the result of interchanging tissue samples in breast cancer. The main focus of the study was to evaluate the applicability of the technique, therefore we studied the samples of a 58-year-old female for whom the result of pathological analysis was reported as 'invasive ductal carcinoma'. The patient was surgically treated by a modified mastectomy technique and referred for chemotherapy. Prior to chemotherapy we found that the tissue samples analyzed did not belong to the patient in question. We used a battery of 15 polymorphic STR loci to identify the sample and we had strong evidence for exclusion of the patient. The analysis was done on both blood and buccal swab of the patient and on the tissue sample. We concluded that the technique is applicable and useful, however care should be taken in the interpretation of the results because the mutations in the tumoral tissues are very well known. Therefore, the maximum of informative loci should be studied and loss of heterozygosity should always be considered. We should also have in mind the possibility of intentional interchange which gives the results value in medico-legal investigations.