How does the mitotic index impact patients with T1 melanoma? Comparison between the 7th and 8th edition of the American Joint Committee on Cancer melanoma staging system

ABSTRACT

Abstract Background: The mitotic index is no longer used to classify T1 melanoma patients into T1a and T1b, so it should not be used to indicate sentinel node biopsy in these patients. Objectives: To evaluate patients with T1 melanoma who underwent sentinel lymph node biopsy and to compare those who were classified as T1a with those classified T1b, according to the 7th and 8th Edition of the melanoma staging system, regarding a positive biopsy result. The authors also aimed to assess whether there is any difference in the results in both staging systems. Material and methods: This was a retrospective analysis of 1213 patients who underwent sentinel lymph node biopsy for melanoma, from 2000 to 2015, in a single institution. Results: Of 399 patients with thin melanomas, 27 (6.7%) presented positive sentinel lymph nodes; there was no difference in positivity for sentinel node biopsy when comparing T1a vs. T1b in both staging systems. Furthermore, the clinical results were also similar between the two groups. However, in the complete cohort analysis, the mitotic index was associated with positivity for sentinel lymph node biopsy (p < 0.0001), positivity for non-sentinel lymph node (p < 0.0001), recurrence-free survival (p < 0.0001), and specific melanoma survival (p = 0.023). Study limitation: Unicentric study. Conclusion: The mitotic index was shown to be a very important prognostic factor in the present study, but it was not observed in patients classified as T1. The mitotic index should no longer be used as the only reason to refer sentinel lymph node biopsy in patients with thin melanoma.