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Cross-contamination of Pathology Specimens: A Cautionary Tale

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Shah et al3 reported a similar case in which a benign granuloma of the lung masqueraded as a squamous cell carcinoma due to histopathologic contamination. Although few similar cases have been described in the literature, the risk posed by such contamination is remarkable, regardless of whether it occurs during specimen grossing, embedding, sectioning, or staining.1,4,5 This risk is amplified in facilities that process specimens originating predominantly from a single organ system or tissue type, as is often the case in dedicated dermatopathology laboratories. In this scenario, it is unlikely that one could use the presence of tissues from 2 different organ systems on a single slide as a way of easily recognizing the presence of a contaminant and rectifying the error. Additionally, the presence of malignant cells in the contaminant further complicates the problem and requires an investigation that can conclusively distinguish the contaminant from the patient’s actual tissue.

In our case, our dermatology and dermatopathology teams partnered with our molecular pathology team to find a solution. Polymorphic STR analysis via polymerase chain reaction amplification is a sensitive method employed commonly in forensic DNA laboratories for determining whether a sample submitted as evidence belongs to a given suspect.6 Although much more commonly used in forensics, STR analysis does have known roles in clinical medicine, such as chimerism testing after bone marrow or allogeneic stem cell transplantation.7 Given the relatively short period of time it takes along with the convenience of commercially available kits, a high discriminative ability, and well-validated interpretation procedures, STR analysis is an excellent method for determining if a given tissue sample came from a given patient, which is what was needed in our case.

The combined clinical, histopathologic, and molecular data in our case allowed for confident clarification of our patient’s diagnosis, sparing him the morbidity of wide local excision on the face, sentinel lymph node biopsy, and emotional distress associated with a diagnosis of aggressive cutaneous melanoma. Our case highlights the critical importance of internal review of pathology specimens in ensuring proper diagnosis and management and reminds us that, though rare, accidental contamination during processing of pathology specimens is a potential adverse event that must be considered, especially when a pathologic finding diverges considerably from what is anticipated based on the patient’s history and physical examination.

The authors express gratitude to the patient described herein who graciously provided permission for us to publish his case and clinical photography.


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