Background: Research on melanocytic nevi predominantly utilizes formalin-fixed, paraffin-embedded tissue, largely limiting research to morphologic and immunohistochemical observations. Withholding portions of fresh nevus tissue for molecular studies could result in the loss of important diagnostic material. Objective: This study prospectively evaluated melanocytic nevi for histologic homogeneity to determine if using a portion for research would have affected diagnosis. Methods: Thirty-three subjects were enrolled in a prospective study in which pigmented lesions were chosen for biopsy on a clinical basis. Lesions were sectioned and each piece submitted in a separate block (mean, 2.7; range 2-5 blocks per lesion). Slides from nevi were examined in two phases. In phase I, sections of nevi were randomized and a diagnosis was rendered for each section of nevus. In phase II, the dermatopathologist reviewed all slides for each nevus as a case, similar to the original interpretation of the lesion provided to the clinician. Diagnoses from phases I and II were compared with the original diagnosis. Results: Case material included 51 melanocytic lesions from 31 subjects. The phase I diagnosis matched the original diagnosis for 99 of 121 slides that showed a melanocytic lesion (82%). The phase II diagnosis matched the original diagnosis for 45 of 51 specimens (88%). Limitations: The study was limited by: a small number of specimens; the clinician could have chosen clinically homogeneous nevi for biopsy; effect of interobserver and intraobserver variability on diagnosis. Conclusions: For the majority of melanocytic nevi in this study, the diagnostic information present in one section of a melanocytic nevus could be extrapolated to the remainder of the specimen without adverse consequences from a diagnostic or therapeutic perspective.
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