BCC is the most common malignancy of the skin. Worldwide, Australia is the country with the highest incidence of this tumor. It is thought that the principal risk factor for the development of BCC is exposure to ultraviolet radiation. Although BCC can be found on any part of the body, the most common locations are in photodistributed areas. Patients who have been treated for psoriasis with psoralens and ultraviolet A light (PUVA) are at a higher risk for developing BCC. Physical risk factors for the development of this tumor include light skin (with a tendency for sunburns instead of tanning), presence of red or blond hair, and blue or green eyes. It is uncommon to diagnose BCC in patients with dark skin. Treatment for prior BCC or for other malignancies with ionizing radiation increases the risk for new tumor formation in the exposed treatment areas. Patients with inherited skin diseases such as xeroderma pigmentosum, Gorlin syndrome (basal cell nevus syndrome), Bazex syndrome, and Rombo syndrome are also at risk for developing BCC. Exposure to environmental arsenic, such as from well water, increases the risk of developing BCC. Prior development of a BCC is also a risk factor for developing additional tumors. Recent studies have shown this risk to be between 33% and 77%.

Studies have shown that the subtype of BCC can be important in prognosis. In general, the nodular and superficial types of BCC are the least biologically aggressive, while the morpheaform, infiltrative, and micronodular subtypes are considered to be aggressive growth pattern tumors, with a greater risk for subclinical extension and recurrence. For this reason, the aggressive growth pattern subtypes of BCC are considered to be high-risk lesions.

Molecular analyses of BCCs have shown mutations in the Patched 1 (PTCH1) gene, which is a component of the Hedgehog signaling pathway. This is the same germline mutation found in patients with Gorlin syndrome. Other genes in this pathway, including Smoothened and Sonic Hedgehog, have also been found to be mutated in BCC. Mutations in the p53 gene have been found in up to 50% of BCCs.

Although BCC rarely metastasizes, it can be locally aggressive as well as destructive, with the potential to invade both soft tissues and bone. In general, a variety of treatment options exist for basal cell carcinoma, including electrodesiccation and curettage, cryotherapy, traditional surgical excision, radiotherapy, and surgical excision utilizing the Mohs micrographic surgery technique.

For most BCCs on the face, Mohs micrographic surgery is the treatment of choice because of its precise control of surgical margins and concurrent maximum viable tissue preservation. Indications for Mohs surgery for BCC include large tumor size (>2 cm), anatomic areas associated with high risk of recurrence (mainly head and neck, especially around the eyes, lips, and ears, i.e., the H-zone of the face), incompletely excised tumors, tumors with aggressive growth pattern histology, such as morpheaform or infiltrative features, tumors with ill-defined borders, recurrent tumors, neurotropic tumors, tumors arising in areas previously treated with ionizing radiation, and the need for maximum tissue preservation. In the case presented here, Mohs micrographic surgery was the treatment of choice for many of the reasons listed above.