Case Number : CT0101 Adam_Bates

If there are, indeed, 20 mitoses per lesion and these are in dermal melanocytes (which they appear to be in the lower left photo), then this is a melanoma, period, no matter what the lesion looks like

The lesion is completely banal and innocent to me, I even could not think of nevoid melanoma. The mitotic figures demonstrated are in the upper half of the dermis. If all are there, I do not find any problem. Mitoses do occur in nevi. May be the lady is pregnant, where increased proliferation of nevi occur. Plus, breast is one of the atypical site nevi... I have also come across this article which might be beneficial
 

Looks very benign at scanning magnification, and there is no obvious phoenotype change or expansion of the papillary dermis (or COE),matures with depth etc. while the mitoses rate is anxiety provoking I wonder if its benign
 

The lesions is simetric in many aspects and there´s maturation. I also believe this is a mitotically active dermal nevus without malignant behavior. Immunostains with HMB-45 and ki-67, which will probably demonstrate higher index in the superficial dermis, might be helpfull.
 

Low ki-67 in the basis of the lesion: Mitotically active dermal nevus, but I would not report like this to not confuse the clinician. I would call it Dermal nevus.
 

I’d call this nevoid melanoma. In addition to the high mitotic index highlighted by Ki-67 immunostain, in the deeper reaches one can find some mitotic figures, some subtle pleomorphic cells with hyperchromatic and enlarged nuclei around an eccrine coil, and a well demarcated pushing lower border. Also, on scanning magnification, the lesion appears more expanded on the right half, but this asymmetry may be an artifact. Anyway, a careful scrutiny of other fields and levels of sectioning will confirm or not this as a nevoid melanoma or a mitotically active Unna’s nevus.
 

If there are, indeed, 20 mitoses per lesion and these are in dermal melanocytes (which they appear to be in the lower left photo), then this is a melanoma, period, no matter what the lesion looks like.
I think this mitotic count is incompatible with a benign melanocytic nevus.
 

The 20 mitotic figures were in 6 cross sections amounting to a total area of 60 mm2. Does this information change your thinking. All mitoses were in the superficial half of the lesion.
 

Yes, a little more than 3 mitotic figures per histologic section, all located in the superficial part of a lesion that looks like benign is not so terrible! I change my mind!
 

Thanks Mark for the additional comment. This was a referred case with no history unfortunately. I reported it as follows: This is indeed the most mitotically active benign naevus I have seen to date. In total, I counted 20 mitotic figures in 6 individual cross sections, amounting to an area of approximately 60mm2. This gives a mitotic rate of far less than 1 per mm, which is in fact low. All of the mitotic figures are superficial and the naevus is otherwise typical, although having rather active appearances, as can be seen in lesions from the breast. Excision is close, but probably complete, and certainly a wait and watch can be adopted.