Value and prognostic significance of mitotic rate in a retrospective series of pT1 cutaneous malignant melanoma patients

INTRODUCTION: Patients affected by thin melanomas (≤1mm) generally have a good prognosis; however, some have a recurrence and eventually die of the disease. The seventh edition of the American Joint Committee on Cancer (AJCC) melanoma staging system, introduced mitotic rate (MR) as one of the primary criteria for staging thin melanoma. MATERIALS AND METHODS: In this study, we sought to determine the prognostic value of mitotic rate in a retrospective cohort of localized primary cutaneous melanoma patients. RESULTS: In total, 286 cases of pT1 primary malignant melanoma occurring in the period 2003-2008 were evaluated. Mitotic counts were re-assessed on standard sections of cases without mitosis and with at least 1 mitosis at diagnosis; 5-year follow-up and recurrence-free survival were available for all patients. Of the 56 radically treated pT1b melanoma patients, 4 (7.1%) had recurrent disease. These data support the efficacy of the incorporation of mitogenicity into AJCC staging for localized cutaneous melanoma and indicate the difficulties in the accuracy and reproducibility of the mitotic count system.