Basal cell carcinoma (BCC) is the most common skin malignancy and it’s incidence is on the increase. Below is a description of the four main different histological growth types and what is features are associated with each of them.
Superficial BCC presents as a scaly, reddish patch ranging in size from a few mm to over 100mm. Due to this clinical appearance there is often confusion with psoriasis. Superficial BCCs are most commonly found on the trunk and account for 10-30% of all BCCs. Histologically they are characterised by superficial collections of atypical basaloid cells projecting from the epidermis or from the sides of adnexal structures such as hair follicles or eccrine ducts. Due to the 2 dimensional processing of histology specimens most superficial BCCs appear multifocal but recent studies using digital imaging techniques show that the tumours nests are actually all interconnected. Truly multifocal superficial BCCs do occur but these are less common.
Nodular BCC most commonly appear as pale, pearly nodules often with macroscopically visible dilated blood vessels coursing over the top of the lesion. Nodular BCCs are most often found on the more sun exposed areas of the body (eg. face and neck). Histologically they are characterised by large, solid lobules of atypical basaloid cells exhibiting a peripheral palisade and often invading as far as the reticular dermis. Other commons features including the classical BCC retraction artefact and tumour cystic degeneration.
Micronodular BCC most often present as slightly elevated/flat pale lesions. They are most commonly found on the back. Histologically, micronodular BCC appears as an invasive BCC with the tumour islands between 3-10 cells in width (approximately the size of a hair bulb). These smaller tumour islands commonly exhibit perineural invasion. Compared to nodular BCC, the excision margins of micronodular BCC can be more commonly underestimated leading to a higher recurrence rate.
Infiltrating BCC presents most commonly as an indurated, pale lesion whose clinical margins appear poorly demarcated. They are mostly found on the face and upper trunk. Histologically they appear as diffuse cords, strands, columns of atypical basaloid cells infiltrating deep into the dermis and that rarely exhibit a retraction artefact or peripheral palisade. Due to the highly diffuse infiltrating nature of this tumour perineural invasion is extremely common therefore recurrences are common.
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