Case Number : Case 2365 - 15 July 2019 Posted By: Raul Perret

Benign fibrous histiocytoma (epitheloid variant ).

My first spot is Atypical intradermal smooth muscle tumor. The subcutaneous location is superficial, and this could be a recurrence. The pseudomyogenic hemangioendothelioma is usually multicentric and show round vesicular, light, poorly atypical nuclei. Moreover PHE doesn't show intersecting fascicules with cigar shaped hypercromatic nuclei, as in this case. Found this article: https://www.ncbi.nlm.nih.gov/pubmed/21358302#

I am not sure about this diagnosis. I think this is a benign tumor. CPC of the previously diagnosis is of course important, so I would suspect that this could be some residual nodule of a congenital melanocytic nevus.

looking at the epidermal reaction, could be a recurrent dermatofibroma/sarcoma

I would consider pseudomyogenic hemangioendothelioma

The final diagnosis was pseudomyogenic hemangioendothelioma. This rare tumor affects mostly young adults and tends to be multifocal but confined to an anatomical region. It is classified as a borderline/intermediate malignancy soft tissue neoplasms (mostly recurring/rarely metastasizing). Morphological findings include chubby spindle and epithelioid cells with eosinophilic cytoplasm and round/oval nuclei with small nucleoli. Neutrophils are frequently seen in the stroma. This tumor has an specific Serpine1-FosB rearrangement that results in overexpression of Fosb that can be demonstrated by immunohistochemistry (and it works quite well). Other typically positive markers include CD31, ERG and CK (AE1-AE3). INI1 (BAF47) expression is retained. 

Great job everyone 

Great case, thanks!