Identification of tumor specimens by DNA analysis in a case of histocytological paraffin tissue block swapping

We report on a patient who was diagnosed with high-grade breast carcinoma by all the pre-surgery clinical evidence of malignancy, but histopathological reports did not reveal any such tumor residue in the post-surgical tissue block. This raised a suspicion that either exchange of block, labeling error, or a technical error took place during gross examination of the tissue. The mastectomy residue was unprocurable to sort out the problem. So, two doubtful paraffin blocks were sent for DNA fingerprinting analysis. The partial DNA profiles (8-9/15 loci) were obtained from histocytological blocks. The random matching probability for both the paraffin blocks and the patient's blood were found to be 1 in 4.43E4, 1.89E6, and 8.83E13, respectively for Asian population. Multiplex short tandem repeat analysis applied in this case determined that the cause of tumor absence was an error in gross examination of the post-surgical tissue. Moreover, the analysis helped in justifying the therapy given to the patient. Thus, with DNA fingerprinting technique, it was concluded that there was no exchange of the blocks between the two patients operated on the same day and the treatment given to the concerned patient was in the right direction.