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

Abstract

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 and mitotic rate (R² = 0.96, P < .0001, β = 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/mm² compared with 3.30 plus or minus 3.54 mitoses/mm² 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.

Keywords: clinical research; guidelines; melanoma; mitotic rate; skin cancer; staging.