Case Number : Case 2551 - 16 April 2020 Posted By: Saleem Taibjee

Apocrine Hidradenoma.

Here is another image

Mixed tumor- epithelial and myoepithelial (hyaline/plasamcytoid cells) predominant with scant stroma, and intravascular nests (which can be seen in mixed tumor)

13 hours ago, Meenakshi Batrani said:

Mixed tumor- epithelial and myoepithelial (hyaline/plasamcytoid cells) predominant with scant stroma, and intravascular nests (which can be seen in mixed tumor)

Thought the same. Maybe I’m wrong and mixed tumor is the right diagnosis. 

glomus tumor

Looks like there  are 2 distinct areas in the tumor:

The last 2 figures show a biphasic tumor composed of peripheral myoepithelial cells, some with a plasmacytoid cytology. The inner luminal layer is composed of columnar cells with probably apocrine differentiation. No cytologic atypia or mitotic activity seen. There is no chondromyxoid stroma to support the diagnosis of a mixed tumor. In the breast, this type of tumor is called adenomyoepithelioma (if benign). Since there is no benign counter part in the salivary glands or lung, it's called epithelial-myoepithelial carcinoma.

The majority of the tumor looks like a poroma and is composed of "poroid" cells (Figure 4 and 5). However, there are also some plasmacytoid cells in the poroma-like component, particularly in the right upper corner of figure 5. One nest is seen in a vessel (which always worrisome, vascular invasion?).

Now the question how to classify this tumor depends on whether the poroid cells are epithelial cells such as in a true poroma or myoepithelial cells. We will need immunohistochemical studies to answer that question (cytokeratinAE1/AE3, S-100, SOX-10, smooth muscle actin, p63 or other myoepithelial markers)

Ductal formation could be encountered in soft tissue myoepithelioma. There is vascular invasion, but I'm not sure how to explain this.

Thanks for this extremely interesting range of comments. I found this case very tricky, and also shared it with Richard Carr. We had a similar conclusion.

The immunostains showed diffuse positive staining with CK5/6 and CK7. Ducts were nicely highlighted by CEA and EMA. p63 was virtually completely negative.

I felt that the poroid component was the more significant, and therefore that the lesion is more akin to hidradenoma territory, but I can see how the images suggest a plasmacytoid myoepithelial component. The lack of p63 staining goes against that. But I would have expected some degree of staining with p63 even if hidradenoma, and this has confused me. The clearly identifiable focus of lymphovascular invasion at the periphery is also concerning. We know that even benign hidradenomas may occasionally show this, and even 'benign metastasis' is described in this context -  see https://www.ncbi.nlm.nih.gov/pubmed/23095508. But even so, this led us to move this into the atypical hidradenoma category, mainly to emphasise the need for clinical follow-up.

Very interesting lesion! I was between poroid hidradenoma and mixed tumor