Case Number : Case 1790 - 07 April - Dr Richard A Carr Posted By: Guest

Another bumper case from Dr Richard A Carr to round of the week nicely.

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melanocytic matricoma

I was thinking of some mixed malignant tumor, with melanoma component ( the two last pic ), like melanocarcinoma or similar, with some sebaceous differentiation too, but after Raul diagnosis I changed my opinion. It's malignant for me, with malignant melanocytes component, so it could be a malignant melanocytes matricoma.

Agree that this small tumor is a Melanocytic Matricoma. The gosht cells are well depicited on picture 6.

From my point of view tumors that have atypical mitotic figures are always or will shortly become malignant. Because this feature means that the neoplastic cells have chromosomal instability. This feature is quite frequent in the few reported melanocytic matricomas so my guess is that they are all/the majority malignant although low grade like in this case. I think, tumors with infiltrative borders, anaplasia and prominent necrosis should better be classified as high grade (instead of current designation as malignant melanocytic matricoma). I would have liked to perform a p53 in a case like this.

Agree with melanocytic matricoma

A follicular tumor with matrical differentiation showing worrisome cellular pleomorphism and high mitotic rate, including some abnormal figures, but otherwise a small lesion with tranquilizing well-circumscribed silhouette at low-power magnification. After a similar case, I remember have reading in Kazakov's book on Cutaneous Adnexal Tumors about neoplasms with discordant cytologic and architectural features, a microscopic eccentricity that suggests benign behavior. So, I favor melanocytic matricoma.

Melanocytic matricoma, malignant.

Great discussion. In my opinion the tumours we have been told look cytologically malignant but are circumscript are probably basically carcinomas in situ. Akin to the very many follicular SCC with pushing/rounded only borders we report on an almost a daily basis now. The authors of cases of melanocytic mactricoma invariably commented on the cytological atypia being discordant with the circumscription (entirely pushing borders) of the tumour. All, wisely in my opinion, recommended complete excision. Therefore malignant melanocytic matricoma becomes nothing more than a pigmented pilomatrical carcinoma in situ with reactive (dendritic) melanocytic cells i.e. one example of a group of tumours lumped variously and imprecisely as basomelanocytic or squamomelanoctyic tumours depending on the way the wind blows on the day. These so-called baso- or squamo- melanocytic tumours for example may be BCC with dendritic reactive melanocytes, follicular SCC with reactive dendritic melanocytes, porocarcinoma with reactive dendritic melanocytes (they can of course look basaloid, squamoid or half-way) etc. Of course the melanocytic component may be malignant giving in my opinion a collision (usually) of the two tumours (epithelial and melanocytic.  I personally am rather doubtful about the very rare cases supposedly showing either immunohistochemical or electron microscopic evidence of epithelial and melanocytic differentiation in the very same cells (i.e. a common progenitor for melanocytic and epithelial differentiation).

So my diagnosis: Malignant pigmented matrical tumour (i.e. pilomatrical carcinoma), pushing only borders, could be regarded as in situ for practical purposes.

I commented that the lesion appeared to have been curetted off completely and I expected a low risk for local recurrence.  Clearly MDM discussion would be warranted but I think watchful waiting would be an acceptable choice.

The idea that this and similar tumours in fact represented in situ variants of pilomatrical carcinoma (and similar sebaceous neoplasms that I've seen personally and other cases that have been pusblished) came to be crystalised in my thinking during our visit to Dr Kazakov's lab in Pilsen in 2016. I think Raul clearly remembers this train of thought as he was also there at the time.