Case Number : Case 2891 - 05 August 2021 Posted By: Saleem Taibjee

Overall silhouette appears to be of SCAP, however, cytology is atypical.  I would consider Syringocystadenocarcinoma papilliferum in situ. Even the lower dermal nodule appears well circumscribed, frank invasion is not evident.  

Nevus sebaceous with syringocystadnoadenocarcinoma papilliferum in situ.

Trichilemmoma + SCAP , both atypical, but I don’t think really carcinomatous. 

4 hours ago, vincenzo said:

Trichilemmoma + SCAP , both atypical, but I don’t think really carcinomatous. 

I also thought of desmoplastic trichilemmoma but couldn't be sure!

SCAP with malignant change

Patient may have nevus sebaceus with syringocystadenoma papilliferum. Background epidermis may be interpreted as Bowen's disease with follicular extension. not really trichilemmoma to me.

Thanks for the comments on this interesting recent case which I did not find straightforward.

I too felt that there were features of syringocystadenoma papilliferum. However, as is often the case with sweat gland tumours, these tumours can be difficult to firmly classify, with possible hybrid features of poroma / hidradenoma (deeper focus) in this case. As you know we can see hybrid lesion in the context of pre-existing naevus sebaceous, but I could not identify this in this case.

With regards to possible dysplasia / malignant change, I found that tricky in this case. I did display an area of more mitotically active / mildly pleomorphic change in the last image above to help stimulate discussion. This area corresponded to a more superficial and eroded aspect of the tumour. I think we not infrequently see such change in the context of poroma lesions, and hence I was not 100% convinced for dysplasia (but could not fully exclude). For interest, p53 is shown below. Although there is quite prominent staining, it does nonethless seem to be wild-type pattern. Following comments above of possible trichilemmoma-like change, I have since requested CD34, but this is negative (not shown).

BW, Saleem