Variability in mitotic figures in serial sections of thin melanomas

Background T1 melanoma staging is significantly affected by tissue sampling approaches, which have not been well characterized. Objective We sought to characterize presence of mitotic figures across a minimum of 5 sequential sections of T1 melanomas. Methods A cohort of T1 melanomas with either 5 (single section per slide) or 10 (2 sections per slide) sequential sections (5-μm thickness) per case were prepared and examined for mitotic figures. Results In all, 44 of 82 T1 melanomas (54%) were classified as T1b. The number of sections with a mitotic figure present ranged from only 1 of 5 sections (n = 5 of 44 cases, 11.4%) to all 5 (n = 20 of 44 cases, 45.5%). A sequential approach versus a nonsequential approach did not appear to matter. Limitation Cases were taken from a single pathology practice in the Pacific Northwest, which may not generalize to other populations in the United States. Conclusion The variation in the presence of mitotic figures within sequential sections supports reviewing 3 to 5 sections to fulfill American Joint Committee on Cancer recommendations. The prognostic significance of a T1b melanoma with a rare mitotic figure on a single section versus a T1b melanoma with mitotic figures on multiple sections deserves more attention to see if further subclassification is possible or even necessary.