Case Number : Case 2746 - 14 January 2021 Posted By: Saleem Taibjee

Merkel Cell/polyomavirus-induced cutaneous carcinoma ( ?primary. Tumor embolism in last fig ). 

Merkel cell carcinoma.

Yes, it has the architecture of a Neuroendocrine Carcinoma but let me add Sebaceous Carcinoma in the differential.  

Nodular and infiltrative lesion in the dermis and subcutis, with tumour cells exhibiting high nuclear-to-cytoplasmic ratio with fine stippled chromatin, multiple small nucleoli and some degree of nuclear moulding. Mitoses/apoptosis frequent. Formation of acini, trabeculae and cords/ribbons. Lymphovascular permeation+.

Agree that we should consider a neuroendocrine tumour, in particular Merkel cell carcinoma of skin (CK20+ CAM5.2+ dot-like paranuclear staining; neuroendocrine marker+).

Have also thought of sebaceous carcinoma though with focal finely vacuolated cytoplasm but can it give rise to this architectural pattern?

Have encountered CK20- neuroendocrine carcinoma of skin, some call it CK20- Merkel cell carcinoma (less commonly associated with Merkel cell polyomavirus) but I am sometimes confused with the terminology. Any thoughts?

Interim update: neuroendocrine markers (CD56, synaptophysin and chromogranin) are negative. Further thoughts?

In that case we have a malignant basaloid tumour.

The white spaces in the image appear strange - probably represent mucin.

Seems that sebaceous carcinoma can show such architecture and should be excluded with adipophillin.

(Less likely with mucin pools)

Thought about a strange-looking BCC, but no conventional appearing areas found from the images. Could still try stains.

Other possibilities include other sweat-gland derived basaloid tumours...

Interested to know thoughts from others.

? Primary Mucinous Carcinoma of the skin...or metastatic..

I am favoring metastatic mucinous carcinoma

I would have called it endocrine mucin producing sweat gland carcinoma but neuroendocrine markers are negative! Although WHO book says it can be variably expressed! What about ER, PR, GCDFP15?

Yes I too favoured this as mucinous carcinoma. It is an unusually ‘solid’ example, rather than the more classical examples of tumour islands within larger lakes of mucin.

This is a recent referral case, courtesy of Dr David Nicholas.

I must admit that my first low power impression was of basal cell carcinoma. But it is on closer scrutiny that one appreciates that the cytology is not quite right and somewhat ‘high grade’, there is a lack of peripheral palisading, and that the mucin is rather striking.

Of course, it is mandatory to consider metastasis in such cases, although primary cutaneous mucinous carcinoma also occurs (most commonly on the eyelid, but can be elsewhere).

This patient has a history of prostate cancer, with an elevated PSA of 50.

Many of the stains were negative. As I mentioned, neuroendocrine markers (CD56, synaptophysin, chromogranin) were negative. BerEP4 was negative, helpful in essentially ruling out BCC. But also negative were: CK20, CEA, TTF1, GCDFP15, CDX2, PSA.

Positive: p63, p53, p16, CK5/6 (patchy), AE1/AE3 (patchy), CK7 (focal), CAM5.2 (focal), EMA (weak patchy).

I have suggested to the referring pathologist to extend the panel to include prostatic acid phosphatase, as well as to review the histology of the original prostate cancer (from 2005).

BW
Saleem

Thanks for sharing this case, Saleem. Quite an interesting one. Important to exclude metastasis from uncommon tumour subtypes for these cases. Wonder if the original prostate pathology shows some rare subtypes like basal cell carcinoma of prostate.

For interest, from experience of readers, do usual primary skin mucinous carcinomas have such basaloid appearance, or the usual adenocarcinoma with more cytoplasm?

Hi Tyelaine. Yes, I think you have a point here. The cytology is somewhat high grade and basaloid compared to the rare examples of primary cutaneous mucinous carcinoma I have come across. I will try to feedback once I hear what the review of the original prostatic histology shows.

BW
Saleem

Thanks, Saleem.

The PSMA stain has now been received and shows some staining within the periphery only. But I think that further supports a cutaneous metastasis from the original prostatic carcinoma.