Mitotic rate as an important prognostic factor in cutaneous malignant melanoma

Recently, the quantification of mitoses in cutaneous melanoma has been discharged from the main prognostic variables of the TNM classification.

To investigate the prognostic value of the presence of mitoses in primary cutaneous melanoma and to establish the number of mitoses per mm² that may have prognostic significance.

A retrospective observational study was performed on 141 patients treated for cutaneous melanoma, who were assessed by the same pathologist, and who had a minimum follow-up of 2 years. Clinical, epidemiological, histopathological and follow-up variables were gathered and compared with the number of mitoses to distinguish the significance of differences by means of univariate, multivariate, and survival analyses.

The cut-off level related to a better sensitivity and specificity was 1.50 mitoses per mm². The presence of two or more mitoses/mm² showed a better relationship with prognostic variables and both the overall and disease-free survival than the presence of 1 or more mitoses/mm². This happens especially in melanomas thicker than 0.8 mm and it could affect the staging in cases with Breslow between 1 and 2 mm.

A mitotic rate of two or more mitoses per mm² in cutaneous melanoma should be considered as a more accurate prognostic factor than one or more mitoses per mm², particularly in tumors equal or greater than 0.8 mm in thickness.