Case Number : Case 2007 - 14 Feb 2018 Posted By: Iskander H. Chaudhry

basal cell carcinoma - peripheral palisading, retraction artifacts.

Don't really see ducts but the silhouette of the tumor makes me think of a poroma.

I thought about poroma too but for above reasons I favor basal cell carcinoma.

Benign basaloid proliferations arising from a follicle. Pilar sheath acanthoma. Dirk Elston calls it a dilated pore of Winer on steroids!

I would go for Poroma too. 

Favoring pilar sheath acanthoma (unusual clinical site and unusual large size). Poroma will not have peripheral palisades.

Favor BCC with eccrine differentiation.

I think it's a poroma group lesion i.e. poroma/hidradenoma. I'd like to see the typical amorphous collagen of these lesions. Occasionally you can look hard and find no lumina. I still favour "pauci-luminal" hidradenoma in those cases that look like this tumour. We can do a little IHC to put nodular BCC to bed (BCC are very characteristically BerEP4 diffuse and strong, EMA completely negative in the basaloid epithelium in >95% of cases). The lesion is mitotic so I sometimes run p53 but hidradenomas can be quite mitotic. I normally recommend complete excision of mitotically active but otherwise benign / indolent adnexal tumours (pilomatrixoma excepted). I might say any mitotically active lesion occasionaly undergoes malignant transformation. I have found some BCC that I have mis-diagnosed as hidradenoma and vice versa. For some reason BCC with pale/clear cells patterns can have markedly reduced BerEP4 and duct like spaces and squamous morular changes very easily confused with hidradenoma. Importantly the BerEP4 should highlight the peripheral palisade in such cases but not in hidradenoma. One should also be cognizant that lesions such as this, that have been sliced across, might give rise to the rare phenomenon of "benign" metastasis (local lymph node involvement) presumably as lesions cells were pushed in to lymphatic during the original procedure.

Poroma