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In this section we have spot diagnoses posted on a daily basis since June 2010, now over 4000! You can review the archived cases and read the suggested diagnoses by users and the final comment by the contributors.
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Case Number : Case 2101 - 26 June 2018 Posted By: Uma Sundram

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8 year old female with solitary lesion on the back. The lesional cells are MITF positive.

Edited by Admin_Dermpath

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I don't know about MITF1-positivity of mastocytosis, but for me it's a mastocytoma 

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Posted (edited)

Yes! Found this: 

Mast cell tryptase and microphthalmia transcription factor effectively discriminate cutaneous mast cell disease from myeloid leukemia cutis

First published: 09 October 2006
Cited by: 7


Background:  Cutaneous mast cell disorders are uncommon, but a subset, especially mastocytoma and mast cell leukemia, can histologically mimic myeloid leukemia cutis. Our objective was to employ a panel of cytochemical and immunohistochemical markers to determine which ones would be most useful in separating these two entities.

Methods:  We stained 17 cases of cutaneous mast cell disease and 20 cases of myeloid leukemia cutis with Giemsa, toluidine blue, or pinacyanol erythrosinate (PE), as well as with antibodies against mast cell tryptase, microphthalmia transcription factor (MiTF), CD117 (c‐kit), myeloperoxidase, CD43, CD25, CD2, and CD68.

Results:  Mast cell tryptase and MiTF emerged as highly sensitive and specific markers for mast cell disease in this context, as both antibodies stained all cases of mast cell diseases but none of myeloid leukemia cutis. Although CD117 stained all cases of mast cell disease, it also stained 2 of 18 cases of myeloid leukemia cutis. PE appeared to be specific for mast cell disease, as 11 of 12 cases stained with this marker, compared with 0 of 18 cases of myeloid leukemia cutis.

Conclusions:  Our results show that mast cell tryptase and MiTF are equally effective in distinguishing mast cell disease from myeloid leukemia cutis.

I'm learning a lot in this site.
Edited by vincenzo

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Raul Perret


Agree, those are mast cells. Thanks for the paper

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Uma Sundram


Yes, mastocytoma. Did not mean to plug myself :)

But it's important to know, especially in this context, that MITF positivity does not mean that this is a melanocytic proliferation.

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