99 10.7 Skin Cancer

Created by CK-12 Foundation/Adapted by Christine Miller

10.7.1 Sunbathing
Figure 10.7.1 I hope they’re wearing sunscreen!

Bathing in Sunshine

Summer sun may feel good on your body, but its invisible wreak havoc on your skin. Exposing the skin to UV light causes photo-aging: premature wrinkling, brown discolourations, and other unattractive signs of sun exposure. Even worse, UV light increases your risk of skin cancer.

What Is Skin Cancer?

Skin is a disease in which skin cells grow out of control. It is caused mainly by excessive exposure to UV light, which damages . Therefore, skin cancer most often develops on areas of the skin that are frequently exposed to UV light. However, it can also occur on areas that are rarely exposed to UV light. Skin cancer affects people of all skin colours, including those with dark skin. It also affects more people altogether than all other cancers combined. One in five Canadians develops skin cancer in his or her lifetime.

Types of Skin Cancer

Skin cancer begins in the outer layer of skin, the . There are three common types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma.

Basal Cell Carcinoma

10.6 Basal Cell Carcinoma
Figure 10.7.2 Basal cell carcinoma

occurs in basal cells of the epidermis. Basal cells are in the layer that divide to form all the keratinocytes of the epidermis. Basal cell carcinoma is the most common form of skin cancer and 1 in 8 Canadians will develop basal cell carcinoma during their lifetime.  A basal cell carcinoma may appear as a pearly or waxy sore, like the one shown in Figure 10.7.2. Basal cell carcinomas rarely spread (or undergo ), so they can generally be cured with a , in which the lesion is cut out of the skin and analyzed in a medical lab.

Squamous Cell Carcinoma

10.7 Squamous cell carcinoma
Figure 10.7.3 Squamous cell carcinoma

occurs in squamous cells of the epidermis. Squamous cells are flattened, -filled cells in upper layers of the epidermis. Squamous cell carcinoma is the second most common form of skin cancer. More than two million cases occur in the United States each year. A squamous cell carcinoma may appear as a firm, red nodule, or as a flat lesion with a scaly or crusty surface, like the one pictured in Figure 10.7.3. Squamous cell carcinomas are generally localized and unlikely to metastasize, so they are usually curable surgically.

 

Melanoma

10.7 Melanoma
Figure 10.7.4 Melanoma

occurs in of the epidermis. Melanocytes are the melanin-producing cells in the stratum basale of the epidermis. Melanoma is the rarest type of skin cancer, accounting for less than one per cent of all skin cancer cases. Melanoma, however, is the most deadly type of skin cancer. It causes the vast majority of skin cancer deaths, because melanoma is malignant. If not treated, it will metastasize and spread to other parts of the body. If melanoma is detected early and while it is still localized in the skin, most patients survive for at least five years. If melanoma is discovered only after it has already metastasized to distant organs, there is only a 17% of patients surviving for five years. You can see an example of a melanoma in Figure 10.7.4.

Melanoma can develop anywhere on the body. It may develop in otherwise normal skin, or an existing mole may become cancerous. Signs of melanoma may include a:

  • Mole that changes in size, feel, or colour.
  • Mole that bleeds.
  • Large brown spot on the skin sprinkled with darker specks.
  • Small lesion with an irregular border and parts that appear red, white, blue, or blue-black.
  • Dark lesion on the palms, soles, fingertips, toes, or mucous membranes.

Skin Cancer Risk Factors

Exposure to UV radiation causes about 90 per cent of all skin cancer cases. The connection between skin cancer and UV light is so strong that the World Health Organization has classified UV radiation (whether from tanning beds or the sun) as a Group 1 carcinogen (cancer-causing agent). Group 1 carcinogens are those carcinogens that are known with virtual certainty to cause cancer. In addition to UV light, Group 1 carcinogens include tobacco and plutonium. In terms of numbers of cancers caused, UV radiation is far worse than tobacco. More people develop skin cancer because of UV light exposure than develop lung cancer because of smoking. The increase in cancer risk due to UV light is especially great if you have ever had blistering sunburns as a child or teen.

Besides UV light exposure, other risk factors for skin cancer include:

  • Having light coloured skin.
  • Having a lot of moles.
  • Being diagnosed with precancerous skin lesions.
  • Having a family history of skin cancer.
  • Having a personal history of skin cancer.
  • Having a weakened immune system.
  • Being exposed to other forms of radiation or to certain toxic substances such as arsenic.

Feature: My Human Body

As with most types of cancer, skin cancer is easiest to treat and most likely to be cured the earlier it is detected. The skin is one of the few organs that you can monitor for cancer yourself, as long as you know what to look for. A brown spot on the skin is likely to be a harmless mole, but it could be a sign of skin cancer. As shown in Figure 10.7.5 below, unlike moles, skin cancers may be asymmetrical, have irregular borders, may be very dark in colour, and may have a relatively great diameter. These characteristics can be remembered with the acronym ABCD.

10.7 ABCDs of skin cancer
Figure 10.7.5 ABCDs of skin cancer

With the help of mirrors, you should check all of your skin regularly. Look for new skin growths or changes in any existing moles, freckles, bumps, or birthmarks. Report anything suspicious or different to your doctor.

If you have risk factors for skin cancer, it’s a good idea to have an annual skin check by a dermatologist. This helps ensure that cancerous or precancerous lesions will be detected before they grow too large and become difficult to cure, or in the case of melanoma, before they metastasize.

10.7 Summary

  • Skin is a disease in which skin cells grow out of control. It is caused mainly by excessive exposure to , which damages . Skin cancer affects more Canadians than all other cancers combined. There are three common types of skin cancer: , , and . Carcinomas are more common and unlikely to metastasize. Melanoma is rare and likely to metastasize. It causes most skin cancer deaths.
  • Besides exposure to UV light, risk factors for skin cancer include having light coloured skin, having lots of moles, and a family history of skin cancer, among several others.

10.7 Review Questions

  1. What is skin cancer?
  2. How common is skin cancer?
  3. Compare and contrast the three common types of skin cancer.
  4. Identify factors that increase the risk of skin cancer.
  5. How does exposure to UV light cause skin cancer?
  6. In which layer of the skin does skin cancer normally start?
  7. Which two skin cancers described in this section start in the same sub-layer? Include the name of the sub-layer and the cells affected in each of these cancers.
  8. Which type of skin cancer is most likely to spread to other organs? Explain your answer.
  9. Which form of skin cancer is the most deadly?
  10. What are some ways people can reduce their risk of getting skin cancer? Explain your answer.

10.7 Explore More

The skin ‘beauty’ and the sun ‘beast’: Charareh Pourzand at TEDxBathUniveristy, TEDx Talks, 2014.

Cancer of the Vulva, Robert Miller, 2014.

How do cancer cells behave differently from healthy ones? – George Zaidan, TED-Ed, 2012.

 

Attributions

Figure 10.7.1

Stolen_Moment_in_the_Sun by Angie Garrett on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.

Figure 10.7.2

Basal_cell_carcinoma,_ulcerated by Kelly Nelson (Photographer) from National Cancer Institute (part of the National Institutes of Health) with the ID 9237 on Wikimedia Commons was released into the public domain (https://en.wikipedia.org/wiki/Public_domain).

Figure 10.7.3

Squamous_cell_carcinoma_(1) by Kelly Nelson (Photographer) from National Cancer Institute (part of the National Institutes of Health) with the ID 9248 on Wikimedia Commons was released into the public domain (https://en.wikipedia.org/wiki/Public_domain).

Figure 10.7.4

Melanoma by Unknown author (Photographer) from National Cancer Institute (part of the National Institutes of Health) with the AV-8500-3850/ ID 9186 on Wikimedia Commons was released into the public domain (https://en.wikipedia.org/wiki/Public_domain).


Figure 10.7.5

ABCDs of skin cancer by CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license. (Original images courtesy of NCI: ID numbers 2362; 2363; 2364; and 2184)

©CK-12 Foundation Licensed under CK-12 Foundation is licensed under Creative Commons AttributionNonCommercial 3.0 Unported (CC BY-NC 3.0) • Terms of Use • Attribution

References

Brainard, J/ CK-12 Foundation. (2016). Figure 5 ABCDs of skin cancer[digital image]. In CK-12 College Human Biology (Section 12.7) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/12.7/

Public Health Agency of Canada. (2019, December 9). Non melanoma skin cancer. Canada.ca. https://www.canada.ca/en/public-health/services/chronic-diseases/cancer/non-melanoma-skin-cancer.html

Robert Miller. (2014, July 22). Cancer of the vulva. YouTube. https://www.youtube.com/watch?v=ID-O-Ion3EQ

TED-Ed. (2012, December 5). How do cancer cells behave differently from healthy ones? – George Zaidan. YouTube. https://www.youtube.com/watch?v=BmFEoCFDi-w

TEDx Talks. (2014, March 28). The skin ‘beauty’ and the sun ‘beast’: Charareh Pourzand at TEDxBathUniveristy. YouTube. https://www.youtube.com/watch?v=60e-t4zglBk

License

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Human Biology by Christine Miller is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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