Introduction

Skin cancer is a disease where abnormal cells in the skin grow uncontrollably, often due to damage from the sun. Skin cancer is prevalent and its rates are going up quickly. While deaths from non-melanoma skin cancer (NMSC) are decreasing, deaths from melanoma, a more serious type of skin cancer, are increasing. Both types of skin cancer cause significant health problems. Non-melanoma skin cancer is mainly caused by long-term sun exposure. In contrast, melanoma often develops due to intense, occasional sun exposure, like getting sunburned during a beach vacation.

The thinning ozone layer has also contributed to the increasing rates of both types of skin cancer. Unlike non-melanoma skin cancer, the relationship between ultraviolet (UV) radiation and melanoma isn't straightforward. This is because people with certain genetic factors have a higher lifetime risk of developing melanoma.^1,2

There are no early signs or precursor lesions for basal cell carcinoma (BCC). However, precursor lesions for squamous cell carcinoma (SCC) include actinic keratoses and SCC in situ. Melanoma can develop from existing benign moles and atypical moles.

How can sunlight cause permanent mutation?

When sunlight, particularly ultraviolet (UV) light, hits the DNA in our skin cells, it can cause damage that leads to mutations. Here is how this process works:

UV light damage

• UV light can break the chemical bonds between two cytosine bases (C) next to each other on a DNA strand
• This break creates a pyrimidine dimer, where the damaged cytosines form new, abnormal bonds with each other.

DNA replication

• During cell division, the DNA strands separate to create new strands.
• Normally, guanine (G) pairs with cytosine (C) (G-T), and adenine (A) pairs with thymine (T) (A-T).

Error introduction

• When the DNA strand with the pyrimidine dimer is used as a template for replication, the disrupted cytosines (C) pair incorrectly with adenines (A) instead of guanines (G).

Continued error

• As the cell continues to divide, the replication error repeats.
• The incorrect pairing (C-A) causes the new strand to have adenines (A) where there should be cytosines (C).
• On the opposite strand, these adenines (A) pair with thymines (T), solidifying a C-T mutation.

Permanent mutation

• Although cells can sometimes repair these errors through ’excision repair’, the C-T mutation can become permanent if not fixed.
• If this mutation occurs in a cancer-related gene, it increases the cell's risk of becoming cancerous.⁴

This process shows how UV light can cause genetic mutations that may lead to skin cancer by permanently altering the DNA in skin cells.

Different types of skin cancer

Basal cell carcinoma (BCC)

Description

• BCC is the most common type of skin cancer
• It usually appears as a small, shiny bump or nodule on the skin, especially in areas frequently exposed to the sun, like the head, neck, or arms

Key point

• It grows slowly and rarely spreads to other parts of the body, but if left untreated, it can cause significant local damage.^5,6

Squamous cell carcinoma (SCC)

Description

• SCC is the second most common skin cancer.
• It often looks like a red, scaly patch, a sore that doesn't heal, or a wart-like growth.
• It typically appears on sun-exposed areas like the face, ears, neck, lips, and backs of the hands.

Key point

• SCC can grow deeper into the skin and spread to other parts of the body if not treated.⁵

Melanoma

Description

• Melanoma is the most dangerous type of skin cancer 
• It can develop in an existing mole or appear as a new, unusual-looking mole
• Melanomas often have irregular shapes and colours and may grow or change over time.

Key point

• Melanoma can spread quickly to other parts of the body, making early detection and treatment crucial.⁷

Actinic keratoses (AKs)

Description

• AKs are not cancer but are considered precancerous. They appear as rough, scaly patches on the skin, often in sun-exposed areas like the face, ears, neck, scalp, chest, backs of hands, or lips.

Key point

• If left untreated, AKs can develop into squamous cell carcinoma.⁸

Risk factors

Several factors can increase the risk of developing skin cancer. These factors can be divided into internal (endogenous) and external (exogenous) categories:

Endogenous (internal)

1. Skin type: People with fair skin that burns easily are at higher risk.
2. Eye colour: Individuals with light-coloured eyes (blue or green) are more susceptible.
3. Hair colour: Those with red or blonde hair are at an increased risk.
4. Moles (Nevi): Having many moles or unusual moles (dysplastic nevi) can increase risk.
5. Personal or family history: If you or a family member have had skin cancer, your risk is higher.

Exogenous (external)

1. Sun exposure: Long-term exposure to the sun, especially without protection, increases risk.
2. Sunburn history: Having had sunburns, particularly blistering ones, raises the risk of skin cancer.
3. Sun protection: Not using sunscreen or protective clothing can lead to a greater risk.

Treatment

The best way to treat melanoma is to catch it early and remove it surgically, ensuring enough of the surrounding tissue is also removed. To determine how far the cancer has spread, doctors perform a sentinel lymph node biopsy. While this technique helps with staging, there currently aren’t any published results from clinical trials that show whether the early removal of affected lymph nodes improves outcomes.

Researchers are exploring new techniques, like magnetic resonance spectroscopy, to assess lymph nodes without invasive surgery. When melanoma spreads locally, surgery remains the most effective treatment. So far, no additional treatments given after surgery have been proven to improve overall survival rates, though many trials are testing new vaccines and immune-boosting therapies.¹³ 

Summary

Preventing both melanoma and non-melanoma skin cancer is very important because catching them early improves the chances of better treatment outcomes. Prevention includes educating people and doctors on how to spot skin cancer early and reducing or avoiding exposure to UV light.² Encourage patients to adopt healthier habits to reduce preventable risk factors.¹² It's crucial to prioritise sun protection and regular skin screenings to reduce the burden of skin cancer.