Reappraisal of the prognostic significance of mitotic rate supports its reincorporation into the melanoma staging system

Background Mitotic rate is a strong, independent prognostic factor in patients with melanoma. However, incorporating it into the melanoma staging system has proved challenging. Methods The prognostic impact of mitotic rate was assessed in a melanoma cohort comprising 5050 patients from 2 geographically distinct populations. Computer‐generated cut points for mitotic rate were constructed to determine its impact on melanoma‐associated survival using Kaplan‐Meier and multivariate regression analyses. The impact of mitotic rate also was assessed in randomly split training and validation sets. Results Mitotic rate had a nonlinear impact on survival, as evidenced by unequally spaced cut points. An index incorporating these cut points that was constructed from one population produced significantly more accurate predictions of survival in the other population than using the entire scale of mitotic rate. An index constructed from the combined cohort was found to be independently predictive of survival, with an impact comparable to that of ulceration. Optimal high‐versus‐low cut points for mitotic rate were generated separately for each T category (