Sampling of melanocytic nevi for research purposes: a prospective, pilot study to determine effect on diagnosis

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.

This study prospectively evaluated melanocytic nevi for histologic homogeneity to determine if using a portion for research would have affected diagnosis.

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.

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%).

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.

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.