Aside from those scary nevoid melanomas or finding a small focus of melanoma arising in a nevus, one other killer tumor to be on the look out for is the Merkel Cell Carcinoma or primary neuroendocrine carcinoma of skin. I’ve looked at some of these tumors at scanning magnification that have looked very much like a basal cell carcinoma, especially in a partially sampled or fragmented lesion, but usually there is some trigger that catches the eye and helps you not miss this diagnosis. Thank your lucky stars for these triggers. One such trigger is found in this biopsy that was sent to us as a basal cell carcinoma clinically. This trigger at low power is the intraepidermal or in situ component, with pagetoid spread of the hyperchromatic cells within the epidermis. This is definitely not a characteristic of a basal cell carcinoma. The cell stain nicely with CK20 in the paranuclear dot-like pattern. There is also staining with synaptophysin, but very little staining with chromogranin. The S100 was negative, which I would also recommend performing on these tumors to help rule out melanoma with neuroendocrine differentiation. The cytology of the cells in this tumor is much different from a basal cell carcinoma, demonstrating finely stippled chromatin and the tumor nests in the dermis do not show peripheral palisading or retraction from the dermis with mucinous stroma. With a good review of this lesion, it is not hard to make the diagnosis. It’s just one of those malignant tumors that keeps you from going too fast.
Am J Dermatopathol. 2004 Jun;26(3):230-3. A case of intraepidermal Merkel cell carcinoma within squamous cell carcinoma in-situ: Merkel cell carcinoma in-situ? Al-Ahmadie HA, Mutasim DF, Mutema GK. Department of Pathology and Laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, OH, USA.