The pigmented BCC is usually nodular or nodulo-ulcerative, ranging in color from light tan to deep brown.

The cystic BCC may attain significant dimensions (Fig. 4.2).

The infiltrating BCC presents as an indurated, yellowish to tan patch or plaque with occasional focal ulceration and poorly defined margins (Fig. 4.3). Patchy crusts, papules, and nodules are scattered throughout some morpheaform tumors. Infiltration within the eyelid can cause deformities and malpositioning of the lid margin.

BCC is characterized by a proliferation of cells with oval nuclei and scant cytoplasm that form infiltrative nests or strands (Fig. 4.4). The neoplastic cells are relatively uniform in appearance and seldom display significant anaplasia or mitotic figures. At the periphery of the nests, they are usually arranged in a radial pattern called “palisading” (Fig. 4.5): although this is not diagnostic, in its absence the diagnosis of BCC should be questioned. The nests of tumor cells characteristically retract from the stroma, creating a gap (Fig. 4.5). Initially thought to be a processing artifact, this gap reflects defects in the production of adhesion-like substances by tumor cells. Necrosis is a common finding in BCC, and the necrotic debris eventually calcifies or is replaced by fibrous scar tissue. BCC also demonstrates an inflammatory infiltrate of variable intensity around the nests of tumor cells that consists predominantly of lymphocytes. The junction between the stroma of the neoplasm and normal connective tissue is ill defined [1].

There is no universally accepted histopathologic subclassification of BCC according to patterns of growth and cellular differentiation. The two most important growth patterns are the circumscribed and the infiltrative. Circumscribed BCC is characterized by nests and sheets of tumor cells and usually corresponds clinically to a nodular tumor. In contrast, an infiltrative BCC is composed mainly of elongated strands of tumor cells that are several cell layers thick, with no peripheral cellular palisading (Fig. 4.6), and usually corresponds to a morphemic variety. However, in many cases different growth patterns occur in the same tumor (Fig. 4.7). There is a third important histologic pattern, the superficial BCC, which is presumed to be of multicentric origin and with horizontal spread. Superficial BCC is described mainly on the trunk and extremities [1]. More than 20 types of cellular differentiation or histologic patterns have been described in BCC as signs of sebaceous, apocrine, or eccrine gland, as well as pillar differentiation in an otherwise typical BCC [1, 6]. However, only the metatypical (basosquamous) carcinomas have an impact on prognosis. Basosquamous carcinoma displays various degrees of squamous differentiation and has been suggested to occupy a conceptual intermediate ground between squamous cell carcinoma and BCC (Box 4.1) [1].

The clinical and histopathologic differential diagnosis is broad. Challenging examples are trichoepithelioma and desmoplastic trichoepithelioma, metastatic carcinoma, sebaceous carcinoma, squamous cell carcinoma, and keratoacanthoma. However, as BCC is by far the most common malignant lesion of the periocular skin, most periocular nodular or cystic skin lesions should be treated as suspicious.

The main treatment modality for BCC is surgical excision of the lesion with microscopic monitoring of its margins or Mohs’ microsurgery [1, 10]. The other surgical and nonsurgical modalities include curettage and electrodessication, cryosurgery, radiotherapy, chemotherapy, photodynamic therapy, and immunotherapy. Selection of the appropriate therapy depends on the patient’s age, anticipated life expectancy, and the location, size, and pattern of growth characteristics of the tumor. However, therapies that are not surgical and do not include microscopic monitoring should be avoided for BCCs when they are not very small, when they are located in the medial canthus, or when the margins are clinically ill defined. The importance of preventing sun exposure needs to be stressed to children and young adults in order to reduce the incidence of BCC in the future [1].