Case Number : Case 3084 - 29 April 2022 Posted By: Dr. Richard Carr

Looks like a nodular hidradenoma to me

?Proliferating Trichilemmal Cyst, with “ancient” changes.

I'll wait for a few more comments. 

After IHC, considering myoepithelial neoplasm- not sure of criteria for primary cutaneous myoepithelioma vs myoepithelial carcinoma vs salivary gland metastasis.

? Hidradenocarcinoma

Strictly speaking the presence of focal ductal differentiation and the squamoid cells favours a myoepithelial-rich chondroid syringoma. Focal confluent necrosis is obviously atypical but there were no other worrying features for malignancy. I shared the case with Luis Requena, Omar Sanqueza and Jason Hornick who are co-authors for myoepithelioma in the next WHO classn who also favoured an essentially benign / low risk lesion. The p16 is mosaic and relatively low Ki67 congruent with p53 were all re-assuring I'm awaiting to hear about IHC for PLAG1 which may  be positive in chrondoid syringoma compared with soft tissue myoepithelioma what often have EWSR1 or FUS re-arrangement. 

17 hours ago, Dr. Richard Carr said:

Strictly speaking the presence of focal ductal differentiation and the squamoid cells favours a myoepithelial-rich chondroid syringoma. Focal confluent necrosis is obviously atypical but there were no other worrying features for malignancy. I shared the case with Luis Requena, Omar Sanqueza and Jason Hornick who are co-authors for myoepithelioma in the next WHO classn who also favoured an essentially benign / low risk lesion. The p16 is mosaic and relatively low Ki67 congruent with p53 were all re-assuring I'm awaiting to hear about IHC for PLAG1 which may  be positive in chrondoid syringoma compared with soft tissue myoepithelioma what often have EWSR1 or FUS re-arrangement. 

Thank you for posting some of these rare and challenging cases, and providing the detailed work-up to arrive at a diagnosis. 

Update from Jason Hornick: Dear Richard, 

IHC for PLAG1 is positive, supporting the diagnosis of a myoepithelial cell-rich mixed tumor.