ABSTRACT
INTRODUCTION: Processing of formalin-fixed, paraffin-embedded (FFPE) tissues is routine practice in the preparation of biopsy specimens for pathological evaluation. Avoiding misdiagnosis due to a mix-up of tissues from different patients requires the utilization of molecular techniques since routine histopathology cannot detect such occurrences, especially if the comingled tissues are of the same type. The Biology Laboratory of the National Center of Forensic Medicine utilizes dedicated forensic procedures to ensure reliable DNA profiles based on short tandem repeats (STR's) from various sample types. These protocols are designed to evaluate even highly degraded samples such as those expected from FFPE tissues. The highly discriminative power profiles are then matched to a reference DNA sample taken from the patient to allow for inclusion or exclusion of the tissue source in question. The following case represents the effective usage of forensic genetics for detection of tissues' cross contamination in FFPE. A 52-year-old female patient was diagnosed with High Grade Dysplasia (HGD) from a sample excised during colonoscopy. DNA extractions taken from FFPE tissues matched the patient. A few additional alleles found in one of the profiles suggested the presence of a residual minor contributor. Out of six embedded tissue fragments, one was found to be a HGD and was marked as such on the slide. The HGD speck was then scraped from the microscopic slide and processed for DNA extraction. The results showed a single DNA profile of a male. Molecular analysis detected a cross contamination of colon tissues. In this case, collaboration between the medical examiner and the forensic laboratory permitted this important discovery that prevented misdiagnosis and possible severe consequences of inappropriate treatment.
