Mitotic rate is associated with positive lymph nodes in patients with thin melanomas

Background: The American Joint Commission on Cancer will remove mitotic rate from its staging guidelines in 2018. Objective: Using a large nationally representative cohort, we examined the association between mitotic rate and lymph node positivity among thin melanomas. Methods: A total of 149,273 thin melanomas in the National Cancer Database were examined for their association of high-risk features of mitotic rate, ulceration, and Breslow depth with lymph node status. Results: Among 17,204 patients with thin melanomas with data on Breslow depth, ulceration, and mitotic rate who underwent a lymph node biopsy, there was a strong linear relationship between odds of having a positive lymph node andmitotic rate (R-2=0.96, P<.0001, beta=3.31). The odds of having a positive node increased by 19% with each 1-point increase in mitotic rate (odds ratio, 1.19; 95% confidence interval, 1.17-1.21). Cases with negative nodes had a mean mitotic rate of 1.54 plus or minus 2.07 mitoses/mm(2) compared with 3.30 plus or minus 3.54 mitoses/mm(2) for those with positive nodes (P<.0001). Limitations: The data collected do not allow for survival analyses. Conclusions: Mitotic rate was strongly associated with the odds of having a positive lymph node and should continue to be reported on pathology reports.