Mitotic rate in melanoma: a reexamination.

We reexamined the relationship between mitotic rate and overall survival in more than 1,200 cases of cutaneous melanoma with long-term follow-up. Like others, we found that mitotic rate was significantly associated with survival (P < 4 x 10(-8)) and more prognostic than tumor ulceration but was not an independent prognosticator because it was significantly associated with tumor thickness and ulceration. Thus, all 3 histologic variables are interrelated; among these, tumor thickness is the most important. Although mitotic rate can be effectively categorized in 3 groups (1/mm2, 1/mm2(-4)/mm2, and > 4/mm2), the optimal way to use mitotic rate remains unclear, and even this simplification requires determining the raw number per square millimeter. Because the collective information provided by tumor thickness, mitotic rate, ulceration, patient age, and site of tumor about hard outcomes such as 5-year fatality is limited and because measuring mitotic rate requires extra time, we recommend that mitotic rate need not be part of routine reports on cutaneous melanoma. Nevertheless, mitotic rate should continued to be measured in academic centers and other sites that maintain large prospective databases on melanoma, and it should be included in further studies of prognosis and adjuvant therapies for cutaneous melanoma.