Basal cell carcinoma

Basal cell carcinoma (BCC) is a malignant neoplasm and the most common type of skin cancer. BCC primarily affects individuals with light skin. Although excessive sun exposure is the primary risk factor, chemicals (e.g., arsenic) and genetic factors also increase the risk of developing BCC. Slow-growing nodules (classic "pearly" appearance) that tend to ulcerate during the course of disease are the characteristic lesions associated with BCC. Surgical excision is the treatment of choice. Because BCC does not metastasize, the prognosis is usually excellent.

• Most common malignant skin tumor
• Incidence: 2–3 million people per year in the US
• Sex: ♂ > ♀ (∼ 2:1)

References:^[1][2]

Epidemiological data refers to the US, unless otherwise specified.

• Sun exposure
• Genetic predisposition
  • Fitzpatrick skin types I and II (people with light complexions, red hair, and who sunburn easily)
  • Albinism ^[3]
  • Xeroderma pigmentosum ^[4]
  • Nevoid basal-cell carcinoma syndrome (Gorlin syndrome): an autosomal-dominant inherited syndrome characterized by the development of multiple basal cell carcinomas at a young age; associated with numerous malformations (macrocephaly, hypertelorism) and neoplasms (medulloblastoma, ovarian cancer)
• Chemicals: arsenic, polycyclic aromatic hydrocarbons (e.g., tars)

References:^[1][5]

• Localization ^[6][7]
  • Typically in areas of skin exposed to sun
  • Basal cell carcinoma of the face typically occurs above the line joining the earlobe and the corner of the mouth
    • Forehead
    • Eyelids
    • Nose and nasolabial fold
    • Upper lip
  • The palms, soles of the feet, and mucous membranes are rarely affected.
• Clinical appearance
  • Pearly nodule with superficial telangiectasia
  • Nonhealing ulcer with a central depression and rolled, nontender borders (rodent ulcer)
  • Scaling plaque (superficial basal cell carcinoma)
• Growth
  • Slow-growing, over months to years
  • Typically painless
  • Locally invasive
  • Very rarely metastasizes

Most basal cell carcinomas occur on areas of sun-exposed skin.

To remember the usual site of occurrence of basal cell carcinoma, think of: “Basal cell carcinoma is more common aBove the upper lip.”

References:^[1][8]

There are several types of basal cell carcinoma:

• Nodular basal cell carcinoma
  • Most common type of BCC
  • Lesions: pearly nodules with a rolled border and central depression
  • Most common site: face (esp. the nose)
• Superficial basal cell carcinoma
  • Lesions: flat, eczematous (scaly) plaque with a pearly border
  • Most common site: trunk

References:^[5][9][10]

Basal cell carcinoma lesions are usually readily identifiable, but the diagnosis should always be histologically confirmed (via full-thickness biopsy done at the edge of the lesion).

• Dermoscopy: initial clinical evaluation of suspected BCC lesions (dermoscopy cannot confirm BCC)
• Excisional biopsy: (full-thickness biopsy or partial-thickness biopsy) first choice
  • Most accurate assessment of the histologic subtype of the tumor
• Wedge biopsies: used to evaluate large lesions

References:^[5][11]

• Histopathology
  • Palisading nuclei: nuclei appear aligned
  • Tumor cells appear similar to epidermal basal cells

References:^[5]

Trichoepithelioma

• Definition: rare, benign tumor of the hair follicle that usually occurs in younger individuals
• Lesions:
  • Skin-colored, firm papules
  • May occur as single or multiple lesions
• Localization: mainly nose and cheeks
• Treatment: excision or laser ablation

Other differential diagnoses

• Keratoacanthoma
• Cutaneous squamous cell carcinoma
• See Differential diagnosis of common skin cancers

References:^[5]

The differential diagnoses listed here are not exhaustive.

• Standard treatment
  • Surgical excision of BCC with a safety margin of surrounding healthy tissue
  • Mohs micrographic surgery: the tumor is removed layer by layer, and each layer is examined for tumor cells.
• Alternatives:
  • Radiotherapy: indicated in
    • Patients who prefer radiotherapy over surgery (esp. elderly patients)
    • Large tumor or locations that are hard to reach
    • After incomplete surgical removal
  • Other options: cryosurgery, laser ablation, and topical chemotherapy with imiquimod or 5-Fluorouracil
    • Indications: small, superficial tumors

References:^[5]

• Excellent prognosis with surgical excision because of the low rate of metastasis