Objectives: To assess interobserver and intraobserver concordance for identifying positive and, negative margins in staged excisions of lentigo maligna and lentigo maligna melanoma and to determine if control biopsy specimens are useful to improve concordance. Design: Retrospective, randomized interobserver and intraobserver comparison study of archived pathologic specimens. The study was conducted in 3 phases, and slides were evaluated blindly and independently by 5 pathologists: in phase 1, all slides were randomized and diagnosed as positive or negative. In phase 2, every third slide was evaluated again and diagnosed as positive or negative. In phase 3, slides were organized into cases, allowing evaluation of each margin in the context of the positive control (tumor from the center of the lesion) and negative control (control biopsy specimen), if available. Setting: University referral center. Study Material: A total of 301 glass microscopic slides from 27 patients who underwent staged excision for lentigo maligna or lentigo maligna melanoma from March 1997 to April 2001. Main Outcome Measures: Interobserver and intraobserver concordance between original diagnoses and study diagnoses rendered on all slides by 5 pathologists. Results: Phase 1 and 3 agreement was moderate (K range, 0.4-0.5). Phase 2 (intraobserver) agreement was moderate to good for all pathologists (K range, 0.6-0.9). Subset analysis revealed a statistically significant increase in agreement with the use of a control strip biopsy specimen for difficult slides. Conclusions: Interobserver concordance for margin analysis in lentigo maligna and lentigo maligna melanoma is moderate, and intraobserver concordance is moderate to good. A control strip biopsy specimen may improve concordance in some cases.
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