Differentials
Microcystic adnexal carcinoma
SIGNS / SYMPTOMS
Also known as sclerosing sweat duct carcinoma, this is a low-grade malignancy derived from sweat (eccrine) ducts, with high recurrence and increased incidence of metastasis. It is well known to simulate morpheaform variants of basal cell carcinoma (BCC), and careful histopathological examination with immunohistochemical work-up might be necessary to distinguish between the two. This type of carcinoma has a higher recurrence rate than BCC and more often necessitates Mohs surgery.
INVESTIGATIONS
Histopathology: there are more ductal structures seen, lined by cuticle of keratin, which are not prevalent in BCCs. It will occasionally be positive with cytokeratin 7 and carcinoembryonic antigen, which are usually negative in BCCs.[53]
Trichoepithelioma/trichoblastoma
SIGNS / SYMPTOMS
Both of these are benign neoplasms of follicular epithelium, with formation of so-called papillary-mesenchymal bodies, follicular units that simulate the bulb of the hair follicle. Other distinguishing features are a lower apoptotic and mitotic rate than seen in basal cell carcinoma, and characteristic split between tumour-associated stroma and dermis (stroma-stroma split).[54][55]
INVESTIGATIONS
Histopathology: the characteristic stroma-epithelium split and increase in apoptotic bodies and mitotic figures is not seen. However, it is not always possible to differentiate these two, especially in the setting of prominent solar damage, and in some cases re-excision will be needed.
Merkel cell carcinoma
SIGNS / SYMPTOMS
On low power/lower magnification, some variants of basal cell carcinoma (BCC) can simulate this highly malignant neoplasm derived from cutaneous neuroendocrine cells.[56]
INVESTIGATIONS
Histopathology: Merkel cell carcinoma presents with opaque nuclei, no nucleoli, and increased nuclear/cytoplasmic ratio. Peripheral palisading might be present.[57]
Immunohistochemical work-up with cytokeratin 20, positive in Merkel cell carcinoma with a characteristic perinuclear dot-like pattern, and high molecular weight cytokeratin cocktail should distinguish it from BCC.
Squamous cell carcinoma (SCC)
SIGNS / SYMPTOMS
Sometimes, especially on the superficial biopsy, it is impossible to distinguish basal cell carcinoma [BCC] (either a metatypical variant of BCC or extensively rubbed BCC) and SCC. Additional sampling, either in a form or larger excisional biopsy, or perhaps complete excision, yields an answer.[3][56]
INVESTIGATIONS
Histopathology: SCC will, at least in some part of the neoplasm, reveal larger cells, with prominent nucleoli, as well as foci of keratinisation and formation of squamous whorls, where the neoplastic cells tightly wrap around each other.
Use of this content is subject to our disclaimer