Mitotic Rate in Cutaneous Melanomas ≤1 mm in Thickness

Abstract

The mitotic rate (MR) of malignant melanoma (MM) refers to the number of mitoses per square millimeter. Studies have suggested that it is an independent prognostic variable predicting survival in patients with MM, and it was recently included in the American Joint Committee on Cancer (AJCC) recommendations for diagnosis and treatment of MM. The AJCC melanoma staging committee recommends using the "hot-spot" approach to determine the MR, whereby it is reported as the maximum dermal mitotic figures identified in a 1-mm area of the melanoma. The AJCC has recommended that the MR be determined in all melanomas, irrespective of Breslow depth or other features. We aimed to quantify the MR in MM ≤1 mm in thickness and to identify statistical associations between the MR, Breslow depth, and Clark level. In addition, we hoped to identify practical issues in determining the MR via the hot-spot technique. We conducted a prospective study to determine the MR, Breslow depth, and Clark level in MM ≤1 mm in thickness. Seven melanomas were identified with epidermal mitoses only (7.4%). Sixteen melanomas had dermal mitoses (16.8%); of these, the majority (75.0%) contained only one mitotic figure. Seventy-nine melanomas had no dermal mitoses (83.2%). Seven lesions (7.4%) demonstrated multiple mitoses; 4 with ≥2 dermal mitoses/mm and 3 with multiple epidermal mitoses. We conclude that thin MM with >1 mitosis/mm is rare and discuss practical and theoretical issues with determining the MR using the hot-spot approach.

Detection of mitotic figures in thin melanomas—Immunohistochemistry does not replace the careful search for mitotic figures in hematoxylin-eosin stain

“…11,12,17,18 In contrast to others, 11,12 we found a high interobserver reproducibility of the mitotic rate with H&E (routine diagnostics vs re-evaluation) with respect to the tumor stage. When comparing the mitotic rate gained by re-evaluation with that gained by routine diagnostics, no switch of the tumor stage from pT1a to pT1b or vice versa was observed.…”

“…This number was low, but compared with other published data, in our cases the mean tumor thickness (0.50 mm) was also low. The mitotic rate increases depending on the tumor thickness, 1,2,7,17 which could also be demonstrated by our data. Some authors reporting higher mitotic rates seem to include the epidermal component of the tumor in the evaluation of the mitoses.…”

Disease-Free Survival for Patients with Thin Melanomas according to the American Joint Committee on Cancer 8th Edition

“…Obviously, baseline characteristics of current series (Table 2) differ from overall MM reports. However, they are similar to previous series including thin MM regarding thickness, ulceration and mitotic rate data [11-13]. The mean thickness for present patients was 0.57 mm [12] and, opposite to general MM series, it was similar for men and women (Table 2).…”

“…The mitotic rate (Table 1) was included as an independent prognosis index by the 7th edition [2, 18, 19]. A previous study reported dermal mitoses in 17% [13] to 20% [12] of thin MM [13], close to the herein reported incidence (24%). None of our patients showed nodal or visceral disease at diagnosis.…”

iDermatoPath – a novel software tool for mitosis detection in H&E‐stained tissue sections of malignant melanoma

“…Thus, based on the modified classification system in 2009 by the AJCC, the correct evaluation of MR in MM, especially in thin melanomas (≤1 mm tumour thickness), seems of high importance. Although the ‘hot‐spot’ method is meanwhile well defined, the correct evaluation of the MR underlies a large inter‐ and intra‐individual variation, even for experienced (dermato‐) pathologists, and the usefulness of this criterion is still a matter of big concern . On the histological side, the identification of a single mitosis can be difficult on haematoxylin and eosin (H&E) slides alone; therefore, additional immunohistochemistry (IHC) is often mandatory, which is a time‐consuming and costly procedure.…”