Basal cell carcinoma is a skin cancer that affects the basal cells. Basal cells are round cells in the epithelium, the outer layer of the skin. Basal cell carcinoma is the most common type of skin cancer.

Basal cell carcinoma, or basal cell skin cancer, is a less aggressive cancer than melanoma. Still, it can grow into nearby tissues and bones if a person does not seek treatment.

Basal cell carcinomas are often flesh-colored, making them less noticeable than some other cancers. A person might notice an unusual lump or bump, a waxy or scaly spot, or a skin-colored growth. There may be multiple changes to the skin or skin lesions.

Regular skin checks and prompt treatment for any unusual growths on the skin can help a person identify basal cell carcinoma early and avoid serious complications. In rare cases, the condition can be fatal.

Read on to learn more about the symptoms, diagnosis, causes, and treatments of basal cell carcinoma.

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The epidermis is the outer layer of skin, formed of several layers of cells. Squamous cells form the outer layer of skin. Basal cells are round cells that sit just beneath squamous cells.

Basal cell carcinoma is one of the two most common types of skin cancer, along with squamous cell carcinoma. Doctors diagnose an estimated 5.4 million cases of these two cancers in the United States each year. Some people develop both types.

Approximately 1 in 5 people in the U.S. will develop skin cancer throughout their lives. According to the American Cancer Society, the vast majority will survive the condition. It reports that around 3.3 million people in the U.S. develop basal cell carcinoma, squamous cell carcinoma, or both each year, but only about 2,000 cases are fatal. Usually, these deaths are among older people who delayed seeking care or people with a weakened immune system.

Some cancers are a risk factor for mortality from other causes. For example, a 2018 systematic review and meta-analysis suggests that people with squamous cell carcinoma are more likely to die of another cause than members of the general population. However, it found no such correlation for basal cell carcinoma.

This suggests that basal cell carcinoma is not a risk factor for or an early warning sign of other diseases.

Doctors have identified at least 26 types of basal cell carcinoma.

Most are amelanotic, which means they do not involve the pigmented melanocytes of the skin, unlike in some other types of skin cancer. Melanocytes are cells that are responsible for producing the pigment called melanin. Therefore, basal cell carcinoma does not usually appear as a mole or other skin discoloration.

The most common types of basal cell carcinoma include:

  • Nodular: This is the most common type. It usually causes raised lesions or nodules on the skin. These lesions may be flesh-colored.
  • Micronodular: The micronodular form is similar to the nodular form in appearance. However, it usually causes multiple smaller nodules instead of a single raised nodule.
  • Superficial: This means that there are multiple cancer cells, but they do not penetrate the dermis, which is the next layer of skin after the epidermis.
  • Morpheaform: This is a more aggressive but less common type of skin cancer. It is more likely to metastasize or spread to another area of the body.
  • Infiltrative: This type tends to spread to the dermis and metastasize to other areas of the body. It is more likely to cause serious complications and can even be fatal.

Most people with basal cell carcinoma have no symptoms other than an unusual growth on the skin. Because basal cell carcinoma does not typically affect melanocytes, it may not cause skin discoloration. This makes it less noticeable than some other types of skin cancer.

Some signs and symptoms include:

  • a nodule or growth on the skin
  • an injury that does not heal
  • an injury that does heal but keeps returning
  • a flesh-colored bump or growth on the skin

Research suggests that basal cell carcinomas grow from immature cells found in the hair follicle. Causes include the following:

UV light

UV radiation from chronic sun exposure can cause basal cell carcinoma via the following mechanisms:

  • UVA: Melanin in the skin absorbs this type of UV light, resulting in the formation of free radicals that damage DNA in skin cells.
  • UVB: This type of UV light can cause direct damage to the DNA and RNA of skin cells.
  • Immune suppression: Exposure to UV can impair the immune surveillance of cutaneous skin.

Learn more about how free radicals affect the body.

Genetic mutations

Like all cancer, basal cell carcinoma happens when cells grow rapidly and out of control.

Mutations in the genes of skin cells caused by DNA damage can lead to this rapid and harmful growth. About 70% of people with basal cell carcinoma have a mutation in the PTCH1 gene.

Some also have mutations in the P53 gene, which is responsible for regulating cell division and cell death. Mutations here can lead to uncontrolled cell growth of cancer cells that can spread to other parts of the body.

Anything that can increase the risk of sunburn and sun-related skin damage can also increase the risk of basal cell carcinoma. Exposure to agents that can cause mutations in human cells may also elevate the risk.

Some important risk factors include:

  • having a fair complexion, especially if a person has red hair
  • developing sunburn easily or a having history of serious sunburns
  • frequent UV light exposure
  • exposure to radiation
  • having a weakened immune system
  • certain genetic conditions, such as Gorlin syndrome, Rombo syndrome, or Bazex-Dupre-Christol syndrome
  • exposure to toxic chemicals, such as arsenic
  • actinic keratosis, which are growths that can cause precancerous changes in the skin

Diagnosing basal cell carcinoma begins with a skin exam.

A doctor can confirm that a person has cancer with a biopsy. A biopsy involves taking a small skin sample and looking at it under a microscope for signs of cancer. In some cases, doctors may perform a biopsy of the lymph nodes or imaging tests if there is concern that cancer has spread to other parts of the body.

Learn more about the different types of skin biopsies.

Basal cell carcinoma looks different in different people. It may appear as:

  • shiny growths
  • a fleshy growth that bleeds or does not heal
  • flesh-colored nodules
  • a crusty growth
  • a growth with blood vessels or spider veins

Basal cell skin cancer is more likely to cause darkly pigmented growths on dark skin.

A person is more likely to notice basal cell carcinoma on areas of the skin that have high sun exposure, such as the face, neck, and shoulders.

Learn more about skin cancer in People of Color.

In most cases, a doctor will recommend removing the growth via a procedure called Mohs surgery. Mohs surgery involves removing thin layers of tissue until all signs of cancer are gone.

Surgery offers the best chances of curing the cancer and preventing it from returning.

Some people cannot safely have surgery and may need radiation therapy, which broadly targets both healthy cells and cancer cells. Because of this, it can cause a number of side effects.

Learn more about the side effects of radiation in people with cancer.

Recurrence rates

The rate at which cancer comes back with various treatments is as follows:

  • Mohs surgery: 1%
  • Surgical excision: 10.1%
  • Electrodessication and curettage: 7.7%
  • Radiation therapy: 8.7%
  • Cryosurgery: 7.5%

Other treatment options

Other options for treating superficial basal cell carcinomas may include cryotherapy, immune response modifiers, or topical chemotherapy.

In cases where the carcinoma has spread, a doctor may use targetted drugs, such as vismodegib (Erivedge). This drug can shrink or slow the growth of cancer.

If targetted drugs do not work as intended, doctors may consider immunotherapy, which can help stimulate the person’s immune system to fight cancer. An example of an immunotherapy drug is cemiplimab (Libtayo).

With treatment, the risk of developing complications from basal cell carcinoma is very low.

Instead, the main risk is that the cancer may come back. Without treatment, basal cell carcinoma can spread to other areas of the body. In rare cases, this can be fatal.

If the cancer grows for a long time without treatment, it may also leave marks on the skin, especially after removal.

Skin cancer affects roughly 20% of people in the U.S at some point in their lives. Basal cell carcinoma is a very common type of skin cancer that can be subtle or cause large growths on the skin. Regular skin checks can help a person detect this type of cancer early, preventing it from growing unchecked.

Basal cell carcinoma is not usually fatal but can be in some cases, especially if a person delays or does not seek treatment.

People should check their skin regularly, monitor skin growths, and see a dermatologist for regular skin exams. Sunscreen, skin protection, and avoiding intense sun exposure can help reduce a person’s lifetime risk of skin cancer.