Based on the above images, what is your first impression?
* Dermatofibrosarcoma protuberans
^Pleomorphic dermal sarcoma
S100 and SOX10
CD34 ❌
CD10 ❌
HMB45 ❌
What are your thoughts now?
* Malignant Peripheral Nerve Sheath Tumour
^ Pleomorphic dermal sarcoma
Melan A and HMB45
PRAME
Adjacent to lesion
HMB45/ Melan A/ PRAME
⚕️Diagnosis:
🔬Spindle cell melanoma
Question
Which if the following is true of spindle cell melanomas?
1/ These tumours are more common in sun effected areas (although any skin site can be affected).
2/ They tend to occur in Caucasian males in the 6-8th decade of life.
pubmed.ncbi.nlm.nih.gov/30250577/
Question
True or false?
Spindle cell melanomas (SCM) are a variant of desmoplastic melanomas (DM).
3/ SCM ae thought to be a distinct entity with different mutations and prognosis.
4/ A suggestion is that a tumour should only be called a DM "if a significant part of the tumour is associated with and dispersed in a dense fibrous stroma".
nature.com/articles/modpa…
Question
Which of the following is true of SCM and their immunohistochemistry/special stains?
5/ SCM usually have strong S100 and SOX10 expression.
6/ Like DM, they can lose HMB45 and Melan A (although less so).
7/ Trichrome stain (see previous article) is useful for DM.
8/ The video below is super useful, cheers @JMGardnerMD !
Question
True or false?
The newish marker, PRAME (PReferentially expressed Antigen in Melanoma), is specific for melanoma?
9/ PRAME can be useful to help distinguish melanocytic nevi ❌ vs melanoma✅
10/ However, it is more marker of malignancy & not specific for any particular tumour (NB sebaceous glands are ✅)
11/ It can be expressed in many tumours, including sarcomas
pubmed.ncbi.nlm.nih.gov/36102613/
Last question
Which of the following genetic mutations is more common in SCM?
12/ The below study showed that BRAF V600E was the most common mutation in SCM (there are others with smaller numbers out there which differ).
13/ Interesting DM tend not to have BRAF mutations, so another difference!
pubmed.ncbi.nlm.nih.gov/22809251/
Spindle cell melanomas on twitter:
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