The Sun's Dark Side:

Understanding Skin Cancer

Welcome!

Skin cancer affects millions of people worldwide, yet many cases are preventable with the right knowledge and precautions. This website is your guide to understanding the main types of skin cancer, how the disease develops, how to identify warning signs and the treatment options available. Whether you want to learn about risk factors, early detection or ways to protect your skin, we’re here to provide clear, reliable information.

After each section challenge yourself with 10 multiple choice questions to reinforce your understanding. Don’t forget to listen to the accompanying podcast for each topic and explore the case studies at the end!

Etiology

Pathogenesis

Signs & Symptoms

Treatment

Case Studies

Learning Outcomes

Identify and distinguish between the main types of skin cancer
Describe the visual characteristics and appearance of each skin cancer type
Recognize the key risk factors that contribute to the development of skin cancer
Compare the severity and behavior of different skin cancers

Overview

Skin cancer is one of the most common forms of cancers that occurs when abnormal cells in the skin grow and divide uncontrollably. Understanding the different types and how they present on the body is essential for early detection and effective treatment.¹

TYPES OF SKIN CANCER

Basal Cell Carcinoma: Develops in the basal cells of the skin and is the most common type of skin cancer.¹

Squamous Cell Carcinoma: Develops in the squamous cells of the skin.¹ ¹¹¹¹

Melanoma: Develops in melanocytes.¹

Basal Cell Carcinoma

Basal cell carcinoma (BCC) is a type of skin cancer that forms in the basal cells of your skin which exists in the lower part of your epidermis which is the outside layer of your skin. This carcinoma looks like a small sometimes shiny bump or scaly flat patch on your skin that slowly grows over time.²

Basal cells: Cells that are responsible for making new skin cells by dividing and copying themselves.

There are 4 main types of Basal cell carcinoma

Nodular: Looks like a round pimple with visible blood vessels surrounding it. It is the most common type of BCC. ³
Superficial: Causes lesions that appear as small shallow marks on your skin that are slightly lighter in color than the surrounding skin. These lesions form on your trunk (torso), arms and legs.³
Morphoeic (sclerosing): Cancerous lesions look like scars that slowly expand over time. This type is most common on your face. This type can also take the form of a small red dot on your skin.³
Pigmented: A rare type that causes hyperpigmentation where an area of your skin becomes darker than the skin surrounding it.³

Nodular

Superficial

Morphoeic (sclerosing)

Pigmented

Squamous Cell Carcinoma

Squamous cell carcinoma (SCC) is the second most common form of skin cancer after BCC. It starts in squamous cells in the outer layer of your skin, the epidermis. SCC usually forms on areas of the skin that receive the most sun exposure like the head, arms and legs. SCC also forms in areas of the body where there are mucous membranes.⁴

There are 2 types of Squamous cell carcinoma

Cutaneous: Cancer that only affects the top layer of your skin (in situ) or cancer that’s spread beyond the top layer of your skin.⁴
Metastatic: Cancer that is spread to other parts of your body beyond the skin.

Cutaneous

Metastatic

Melanoma

This is the most dangerous type as it grows quickly and has the ability to spread to any organ. Comes from skin cells called melanocytes. These cells produce melanin, the dark pigment that gives skin its color. Melanoma forms on the eyes and internal organs.⁵

There are 2 types of Melanoma

Acral lentiginous melanoma: Appears as a small, flat spot of discolored skin that is often dark brown or black. It usually grows outward across the surface of the skin for a long time before it starts to grow down into the skin.6
Superficial spreading melanoma: Tends to grow outward (called radial growth) and spread across the surface of the skin. But it can also start to grow down into the skin (called vertical growth). It is often flat and thin (less than 1 mm thick) with an uneven border.6

Acral lentiginous

Superficial spreading

Rare Types of Skin Cancer

Merkel Cell Carcinoma

Develops in the Merkel cells found in the outer layer of the skin (epidermis)
Exposure to UV light, weak immune system and viral infection may cause these cells to become cancerous and grow uncontrollably.7
Tends to spread to other parts of the body such as lymph nodes.7
Shiny lumps most commonly appear on the face, neck, arms or eyelids.7
Stage 0 = affects outer layer. 7
Stage IV = indicates cancer in distant organs. 7

Kaposi Sarcoma

A type of soft tissue sarcoma
It causes lesions that form on the skin or mucus, membranes that line the inside of the nose, mouth and anus.8
These tumors may also develop in the lining of internal organs like the lungs and liver.8
One is prone to get Kaposi Sarcoma if they carry Human Herpesvirus 8 (HHV-8) and have a weakened immune system.8

Sebaceous Gland Carcinoma

An aggressive malignant tumor that starts in the skin’s oil producing (sebaceous) glands.9
The most common site are the eyelids.
It can reoccur after treatment for many individuals.9

Podcast:

(Open in preview)

The_Internal_Architecture_of_Skin_Cancer.m4a

Test Your Knowledge

1. Which layer of the skin does Basal Cell Carcinoma originate from?

A) The outer surface of the epidermis

B) The lower part of the epidermis

C) The dermis layer beneath the skin

D) The subcutaneous fat layer

2. What is the most serious type of the three main skin cancers?

A) Basal Cell Carcinoma

B) Squamous Cell Carcinoma

C) Merkel Cell Carcinoma

D) Melanoma

3. What does melanin do for the skin?

A) Produces new skin cells

B) Lines the inner organs and body cavities

C) Gives skin its color and offers some UV protection

D) Regulates oil production in sebaceous glands

4. Which type of Basal Cell Carcinoma looks like expanding scars and is most common on the face?

A) Nodular

B) Superficial Spreading

C) Pigmented

D) Sclerosing

5. Where does Squamous Cell Carcinoma most commonly form?

A) The lower back and abdomen

B) Internal organs only

C) Areas with the most sun exposure like the head, arms, and legs

D) The sebaceous glands beneath the skin

6. What does metastatic Squamous Cell Carcinoma mean?

A) Cancer only in the top layer of skin

B) Cancer that forms exclusively in mucous membranes

C) Cancer limited to the epidermis

D) Cancer that has spread beyond the skin to other parts of the body

7. Which type of melanoma tends to grow outward across the skin's surface before growing downward and is often flat and thin?

A) Acral Lentiginous Melanoma

B) Nodular Melanoma

C) Superficial Spreading Melanoma

D) Pigmented Melanoma

8. What virus is associated with Kaposi Sarcoma?

A) HPV (Human Papillomavirus)

B) HIV (Human Immunodeficiency Virus)

C) HHV-8 (Human Herpesvirus 8)

D) EBV (Epstein-Barr Virus)

9. Which skin cancer most commonly affects the eyelids and originates in oil producing glands?

A) Merkel Cell Carcinoma

B) Kaposi Sarcoma

C) Melanoma

D) Sebaceous Gland Carcinoma

10. Which of the following is a risk factor for Merkel Cell Carcinoma?

A) High sugar diet and lack of sleep

B) Carrying HHV-8 and low blood pressure

C) UV light exposure and a weakened immune system

D) Excess melanin production and dry skin

Answer Key

References

Cleveland Clinic. Skin Cancer Overview. Cleveland Clinic [Internet]. Cleveland Clinic. 2021. [cited 2026 April 10]. Available from: https://my.clevelandclinic.org/health/diseases/15818-skin-cancer

Mayo Clinic. Basal Cell Carcinoma - Symptoms and Causes [Internet]. Mayo Clinic. 2025. [cited 2026 April 10]. Available from: https://www.mayoclinic.org/diseases-conditions/basal-cell-carcinoma/symptoms-causes/syc-20354187

Basal Cell Carcinoma [Internet]. Bccancer.bc.ca. 2025. [cited 2026 April 10]. Available from: https://www.bccancer.bc.ca/books/skin-cancer-prevention-early-diagnosis-courses/course-readings/skin-cancer-early-diagnosis-readings/basal-cell-carcinoma

Mayo Clinic. Squamous Cell Carcinoma of the Skin - Symptoms and Causes [Internet]. Mayo Clinic. Mayo Clinic; 2023. [cited 2026 April 10]. Available from: https://www.mayoclinic.org/diseases-conditions/squamous-cell-carcinoma/symptoms-causes/syc-20352480

Mayo Clinic. Melanoma - Symptoms and Causes [Internet]. Mayo Clinic. Mayo Clinic; 2023. [cited 2026 April 10]. Available from: https://www.mayoclinic.org/diseases-conditions/melanoma/symptoms-causes/syc-20374884

Cancer C. Types of melanoma skin cancer [Internet]. Canadian Cancer Society. 2015. [cited 2026 April 10]. Available from: https://cancer.ca/en/cancer-information/cancer-types/melanoma-skin/what-is-melanoma/types-of-melanoma

Merkel Cell Carcinoma: Symptoms, Treatment & Prevention [Internet]. Cleveland Clinic. 2022. [cited 2026 April 10]. Available from: https://my.clevelandclinic.org/health/diseases/17971-merkel-cell-carcinoma

Cancer CCS / S canadienne du. Kaposi sarcoma [Internet]. Canadian Cancer Society. [cited 2026 April 10]. Available from: https://cancer.ca/en/cancer-information/cancer-types/soft-tissue-sarcoma/what-is-soft-tissue-sarcoma/types-of-soft-tissue-sarcoma/kaposi-sarcoma

Sebaceous Carcinoma: Symptoms, Causes & Treatment [Internet]. Cleveland Clinic. [cited 2026 April 10]. Available from: https://my.clevelandclinic.org/health/diseases/24087-sebaceous-carcinoma

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