Basal Cell Carcinoma

Overview

By Tina Shahian, PhD

Basal cell carcinoma is a type of skin cancer that occurs in the basal cells of the epidermis – the outermost layer of the skin. Basal cells constantly divide to replace dead or damaged skin cells closer to the outer surface of the epidermis. However, these cells can become cancerous when exposed to ultraviolet (UV) radiation or other factors, triggering them to proliferate uncontrollably. Basal cell carcinoma is the most common type of cancer with nearly 2.8 million Americans affected every year. 

Basal cell carcinoma is usually found on the head and neck, but can be found anywhere on the body, including the limbs. Unlike more aggressive cancers, basal cell carcinoma rarely spreads, or metastasizes, to other sites within the body. Timely treatment and removal are key interventions to avoiding deformity of the affected area, and spread into deeper tissues. This cancer is fully treatable if detected early, but the chance of reoccurrence in the same area or other areas of the body is high.

Causes and Risk Factors

Drawing of skin cross-section showing epidermis

Like all cancers, basal cell carcinoma is a result of errors, or mutations, in the DNA of affected cells.  While some mutations are harmless, others dismantle the cellular pathways that control cell proliferation. In the absence of tight controls, cells overgrow to form tumors. The main cause of DNA damage in basal cell carcinoma is prolonged exposure to UV light from the sun. UV radiation is also believed to block DNA repair proteins, further allowing the proliferation of mutant cells. The following risk factors are associated with basal cell carcinoma:

  • UV Radiation. Of the three types of UV radiation (A, B, and C), UVB radiation is linked to skin cancers. Chronic exposure to UV radiation from the sun or tanning beds, especially before the age of 18, increases the chance of developing basal cell carcinoma. Living in the sunny regions of the globe is also associated with a higher risk.
  • Other radiation. Exposure to X-rays (used to treat some skin conditions) can cause basal cell carcinoma.
  • Gene mutation. Mutations in the genes of specific proteins are linked to basal cell carcinoma. These include mutations in the tumor suppressor proteins p53 (TP53) and patched homologue 1 (PTCH1); sonic hedgehog (SHH); and smoothened (SMO).
  • Arsenic. Exposure to arsenic, a toxic metal, through ingesting contaminated water or farming and refinery occupations, can cause basal cell carcinoma.
  • Skin color. Light-skinned individuals absorb a greater amount of the damaging UV rays from the sun and, therefore, carry a greater risk for skin cancers.
  • Age and gender. Basal cell carcinoma is common in individuals over the age of 50, and more so in men.
  • Immune suppressive therapy. Basal cell carcinoma can form in patients on immuno-suppressant drugs following an organ transplant, or due to other medical conditions.
  • Personal and family history. Once an individual has been diagnosed with basal cell carcinoma, they have much greater chance of developing it a second time. A family history of the cancer is also associated with higher risk.
  • Inherited syndromes. Nevoid basal cell carcinoma syndrome (Gorlin-Goltz syndrome) and xeroderma pigmentosum are rare inherited diseases that increase susceptibility to basal cell carcinoma.

Symptoms

Basal cell carcinomas are most often found on the face, neck, and scalp; however, a physician should also examine any unusual bumps and sores in other areas of the body. A basal cell carcinoma may display the following symptoms:

  • A white to yellow, waxy growth with visible blood vessels
  • A pink, skin-colored, or brown growth with a flat center
  • A sore with a sunken center that bleeds easily and does not heal
  • A sore that oozes or crusts over.

Diagnosis and Treatment

In order to diagnose a basal cell carcinoma, the physician examines the affected area and removes a sample (biopsy) for additional evaluation. Once a positive diagnosis is made, the following treatment options are available:

  • Excision. Depending on the size of the carcinoma, surgery is used to cut and remove the affected cells, as well as some of the surrounding healthy cells. Minor reconstructive surgery is often required to repair the appearance of the treated area.
  • Electrodesiccation and curettage (ED&C). In this procedure, small carcinomas on the ear and leg are scraped away and remaining cancerous cells are killed using electricity.
  • Cryosurgery. Thin cancers that occur on the skin surface can be frozen (killed) using liquid nitrogen.
  • Mohs surgery. In this technique, a thin layer of cells is removed and examined under a microscope for the cancer phenotype. These steps are repeated until only healthy cells are observed. Mohs surgery is a precise and effective way to remove large, deep carcinomas, without removing an excessive amount healthy tissue.
  • Radiation. X-ray beams can be used to kill basal cell carcinoma cells. This method is very effective but carries the associated risk of additional exposure to radiation.
  • Topical creams. When excision is not an option, topical drugs are used to locally treat basal cell carcinomas. For example, imiquimod and fluorouracil destroy cancer cells by using the body’s own immune system and interfering with DNA replication, respectively.
  • Oral therapy. Vismodegib is the only FDA-approved drug for the treatment of advanced basal cell carcinoma. It is an oral drug that inhibits proliferation of basal cell carcinomas.

Prevention

The best way to prevent basal cell carcinoma is by minimizing exposure to harmful radiation from the sun and other sources.

  • Avoid the midday sun (10 a.m. to 4 p.m.).
  • Wear sunscreen with broad UVA/UVB protection.
  • Cover exposed skin with protective clothing.
  • Tanning in direct sun or tanning beds is not advisable.

Routine self-examination of the skin for abnormal growth and sores is critical, especially for individuals with a high risk for basal cell carcinoma.

Sources

  • “Skin Cancer: Basal and Squamous Cell”. American Cancer Society. Feb 2014. Retrieved Jun 26, 2014. http://www.cancer.org/cancer/skincancer-basalandsquamouscell/detailedguide/skin-cancer-basal-and-squamous-cell-what-is-basal-and-squamous-cell.
  • "Basal cell carcinoma". Mayo Clinic. Mayo Foundation for Medical Education and Research. Sep 2013. Retrieved Jun 26, 2014. http://www.mayoclinic.org/diseases-conditions/basal-cell-carcinoma/basics/definition/con-20028996.
  • "Basal Cell Carcinoma (BCC)”. Skin Cancer Foundation. Retrieved Jun 26, 2014. http://www.skincancer.org/skin-cancer-information/basal-cell-carcinoma.
  • “Basal cell carcinoma”. American Academy of Dermatology. Retrieved Jun 26, 2014. http://www.aad.org/dermatology-a-to-z/diseases-and-treatments/a---d/basal-cell-carcinoma.