Basal Cell Carcinoma of the Skin Generalities

Basal cell carcinomas (BCCs) are believed to arise from the basal layer of epidermis and its appendages;
- Since they arise from hair follicles:
  - Most lesions are found on sun-exposed areas of hair-bearing skin
These tumors tend to grow slowly:
- But when left untreated can lead to invasion of local structures, including:
  - Muscle, cartilage, and bone
Although BCC is characterized by local and sometimes destructive invasiveness:
- Metastasis is rare:
  - Occurring in less than 0.05% of cases
A number of risk factors are associated with the development of BCC:
- Ultraviolet (UV) solar radiation is considered to be a significant risk factor:
  - Development is thought to arise from intense, intermittent sun exposure:
    - Leading to burns
  - BCC tends to occur in the head and neck area
- BCC tends to occur in the treatment field of previous radiation therapy (RT):
  - Specially at a young age
- Settings of immunosuppression, such as:
  - Organ transplantation, HIV infection, or long-term glucocorticoid:
    - Increase the incidence of BCC
Anatomic location within the high-risk “H zone” or “mask area” of the face and size are:
- Risk factors for BCC recurrence and metastasis

Extensive research has led to advances in understanding the genetics of BCC:
- The sonic hedgehog pathway plays a crucial role in the pathogenesis of BCC:
  - Mutations in this pathway have been implicated in the development of disease
- Mutations in the PTCH1 (patched 1) gene on chromosome 9q:
  - Which codes for the sonic hedgehog receptor:
    - Are present in 30% to 90% of sporadic BCCs
Patients with genetic syndromes, including:
- Xeroderma pigmentosum, albinism, Muir-Torre syndrome, Fanconi anemia, nevoid basal cell carcinoma syndrome or Gorlin syndrome, and Li-Fraumeni syndrome:
  - Have an increased incidence of squamous cell carcinoma (SCC) and BCC