Case Number : Case 2744 - 12 January 2021 Posted By: Iskander H. Chaudhry

Great resource and virtual slide is quite nice.

My first few attempts so hopefully reasonable.

Nodular pushing growth from epidermis down to the deep subcutis. Tumour cells are non-pigmented pleomorphic with eosinophilic/finely vacuolated cytoplasm, spindled and form fascicles. Mitoses is frequent. Very rare suggestion of some abortive tiny lumens in the cytoplasm. No definite necrosis. Small amount of accompanying lymphoplasmacytic infiltrate. Adjacent solar elastosis. Seems no definite in-situ lesion in the epidermis. No definite ulceration. No perivascular or perineural invasion.

Looks like a spindle cell tumour - probably need immunos to help in the diagnosis. May also be limited by biopsy specimen - may need to correlate with excision. Need to first exclude diagnoses such as angiosarcoma (spindle cell variant), may help with ERG+ (or other vascular markers). Sebaceous carcinoma, with expression for adipophillin (but seems classically less spindled?). Other differentials including amelanotic melanoma (spindle cell) (SOX10+ or other melanocytic markers), spindle cell carcinoma (may express some epithelial markers), etc. Will need to consider atypical fibroxanthoma (spindle cell variant)/pleomorphic dermal sarcoma after exclusion of other possibilities.

Interested to know the approach and views from other participants.

Malignant spindle cell neoplasm.

Very instructive description by tyelaine

My differentials are: Spindle cell SCC, AFX and Melanoma (probably in that order)

Virtual slide is so nice

Congratulations to the DermpathPRO team for introducing the innovation of digitally scanned slides to the SpotDiagnosis section.

I agree with earlier comments regarding the differential diagnosis of this mitotically active, malignant spindle cell tumour. 

It doesn't seem pleomorphic enough for a typical AFX, or sufficiently penetrating for a pleomorphic dermal sarcoma.

I would be inclined towards atypical intradermal smooth muscle tumour (leiomyosarcoma). Obviously immunohistochemistry is necessary to settle the issue.

I did it!!! TKS @Richard Logan

My bet is for spindle SCC however agree with all the DD. 

Favor atypical intradermal smooth muscle neoplasm...

Favor Spindle Cell Melanoma

I tend to limit my panel in "malignant" spindle cell tumours (on biopsy) in severe sun-damaged skin to Pan-keratin, p63, S100, CD10 for histogenesis. I've been adding p53, p16 & Ki67 for "malignancy" if the differential is with a scar or some benign fibrohistiocytic proferation (not relevant here).

Here I see some subtle nesting of the theques and would think melanoma first.

To be controversial as long as it's excised with clear margins the diagnosis is irrelevant until it metastasises (which vast majority won't in my experience) and even then (if it's melanocytic) most melanomas on severely sun-damaged skin are BRAF mutation neg. Anecdotally we're seeing a high rate, in malignant spindle lesions on severely sun-damaged skin, of p16 null and a high rate of either null or markedly up-regulated p53 but this would require a formal study.

Totally agree with Dr Carr. I also add sma & desmin in my panel. 

Well done all - it was a spindle cell Melanoma with diffuse S100 protein staining.