Under your skin: How melanoma grows

Posted on 13 December 2019

Melanoma is the most common malignancy in the world, affecting men and women of every skin colour. Here’s how it develops.

How skin cancer grows

The development of skin cancer is unfortunately still not fully understood, says Dr Dilshaad Asmal, a dermatologist at Mediclinic Cape Town. “However, the literature is starting to show that along with ultraviolet radiation and immune suppression, genetic and molecular alterations are also involved in the process,” she says. Our body’s largest organ, the skin is made up of the epidermis (the outer layer), the dermis (the second layer) and subcutaneous tissue (the bottom layer). The epidermis contains squamous cells, basal cells and pigment-producing melanocytes. Constantly exposed to UV radiation from the sun, specifically UVB radiation, which is the major environmental cause of skin cancer, the epidermis is highly susceptible to DNA damage. This damage causes skin cells to start acting abnormally and to mutate. In the case of melanoma, the deadliest form of skin cancer, melanoma cells originate from melanocytes. Non-melanoma skin cancer includes basal cell skin cancer, the most common type and the least dangerous, and squamous cell skin cancer, the second most common type. Squamous cell carcinomas (SCC) develop from squamous cells, while basal cell carcinomas (BCC) originate from basal cells. If the immune system can’t keep these abnormal cells under control, they keep mutating and divide uncontrollably, forming growths and lumps called tumours, below and on the surface of the skin. These tumours are either benign (non-cancerous) or malignant (cancerous).



After Australia, South Africa has the second highest incidence of skin cancer with regards to caucasians.

How non-Melanoma skin cancers grow

Easier to treat, BCC and SCC grow more slowly than melanomas. “They show different behaviours, growth and metastatic (see below) capabilities from each other,’ says Dr Asmal. “They usually start off as the pre-cancerous condition actinic keratosis, which presents as a red, scaly, rough area of skin, and develop on areas regularly exposed to the sun. SCC can also appear in unexposed areas.” They can present differently too, for example, BCC can have brown pigment within the rough patch, while SCC may have a spiky horn sticking up from its surface. If left untreated, both BCC and SCC can start bleeding and turn into tumours – and can eventually lead to considerable skin damage, Dr Asmal says. BCC very rarely spreads, but SCC can metastasise to your lymph nodes and organs, if left untreated, but there’s a low risk of that occurring, says Dr Asmal. “Fortunately both BCC and SCC have an excellent prognosis and if they’re caught early, an excision of the whole tumour will be all that is needed,” confirms Dr Asmal.


How Melanoma grows on the skin

Melanoma only comprises 5 to 10% of the skin cancers diagnosed, but it’s responsible for 75% of all deaths from skin cancer. It’s highly metastatic, drug-resistant and notoriously aggressive. Melanoma tends to present as a new mole or a change in appearance of an old mole. To spot a melanoma, doctors use the ‘Ugly Duckling’ sign and the ABCDE rule. “The Ugly Duckling sign works on the concept that most moles on the body resemble one another, while melanoma stands out in comparison and grows into an ugly duckling,” explains Dr Asmal.


The ABCDE rule identifies these warning signs:



What happens when skin cancer metastasises?

Metastasis is when cancer cells spread from where they began in the primary tumour in the epidermis and begin to penetrate deeper into the layers of skin, reaching the blood vessels and lymph nodes of the dermis, allowing malignant cells access to your entire system. They travel through your lymph system or blood, forming a metastatic tumour in another part of your body, such as your lungs or brain. When melanoma metastasises, you may experience a variety of symptoms, depending on where in the body it has spread. For example, if it’s in your lymph nodes, you may get swollen lymph nodes in your neck, or you may cough up blood if it’s spread to your lungs. Jaundice may be a symptom if it’s moved into your liver and serious back pain may indicate that it’s spread to your bones.


Treatment options for non-Melanoma cancers

When detected early, most BCC and SCC can be treated and cured.


Surgical excision: The tumour and some surrounding tissue are removed surgically.

Mohs micrographic surgery: The tumour is cut from the skin in thin layers. Each layer is checked for cancer cells and then more layers are cut if needs be.

Curettage and electrosurgery: This removes low-risk lesions with a curette, a spoon-shaped instrument with a sharp edge, followed by heat from an electrical current or a chemical agent to seal the wound.

Cryotherapy: Low-risk lesions are frozen off with liquid nitrogen.

Photodynamic therapy: This treatment uses a drug and a certain type of laser and sunlight to kill cancer cells.

Topical medications: These are creams or gels applied directly to affected areas of the skin to treat superficia lesions. . Oral medications: These are drugs that are taken orally to treat advanced BCC.

Radiation: Using high-energy rays or particles to destroy cancer cells, this is generally offered when surgery is not an option or the cancer is advanced.

Chemotherapy: Used for high-risk non-melanoma cancer, anti-cancer drugs travel through the bloodstream to destroy cancer cells.

Targeted therapy: These are drugs used to target rare cases of advanced BCC and SCC.


Approximately 20 000 South Africans are diagnosed with non-melanoma cancers every year and approximately 1 500 South Africans are diagnosed annually with melanoma. On average, 700 people die from the disease every year.


Melanoma at different stages

Treatment will depend on where the tumour is, its staging and your general health and level of fitness says Dr Asmal.


Early stage: The cancer is only in the skin where it started and hasn’t spread. It includes stage 0, 1A, 1B, 2A, 2B and 2C.

Locoregional: The cancer has spread to nearby lymph nodes, or to nearby areas of skin or lymph vessels. This is stage 3 melanoma.

Metastatic means that the cancer has spread farther from its origin. It’s known as stage 4.



Surgery: Normally the sole treatment needed for early stage melanoma, it’s also used alongside other treatments for more advanced stages. A sentinel lymph node biopsy may be needed; a lymph node is removed to check if melanoma has spread into your lymph nodes.

Immunotherapy (aka biologic therapy): This class of medicines helps boost the immune system to help kill cancer cells and is used in advanced stages. It includes oncolytic virus therapy, where viruses are altered in the lab to kill cancer cells.

Targeted therapy: These drugs target parts of melanoma cells that make them different from normal cells. They include drugs like BRAF inhibitors and MEK blockers, which are generally used for metastatic cancer.

Chemotherapy: Used for advanced cancer, chemotherapy is used if you’re unable to have a targeted cancer drug or immunotherapy.

Radiotherapy: Radiation will be used on specific sites of melanoma, for example, in the lungs or brain, and is generally only for stage 4.




If you are concerned about any changes in your skin or moles, schedule an appointment with one of Mediclinic’s expert dermatologists.

Mediclinic hospitals, day clinics and staff are ready to welcome you for your regular doctor’s appointments and screenings.

Published in Cancer

In the interest of our patients, in accordance with SA law and our commitment to expertise, Mediclinic cannot subscribe to the practice of online diagnosis. Please consult a medical professional for specific medical advice. If you have any major concerns, please see your doctor for an assessment. If you have any cause for concern, your GP will be able to direct you to the appropriate specialists.

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