Variability in mitotic figures in serial sections of thin melanomas.

ABSTRACT

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.