Skin Cancer: Warning Signs, the ABCDE Rule and Treatment
Skin cancer is a cancer that develops from abnormal growth of skin cells. There are 3 main types that are commonly seen: BCC, SCC and melanoma. The good news is that most skin cancers can be treated very successfully when found early, and in many cases they can be cured completely. This article explains the types of skin cancer, the warning signs according to the ABCDE rule, and the treatment options, to help you notice changes in your skin and moles sooner.
How many types of skin cancer are there?
The skin cancers seen most often fall into 3 main types, which differ in severity and appearance:
BCC (Basal Cell Carcinoma): The most common type, with low severity. It usually grows slowly and rarely spreads to other organs.
SCC (Squamous Cell Carcinoma): Moderate severity, with a higher chance of spreading than BCC.
Melanoma: The most serious type of skin cancer. It can spread to other organs if found late, so it needs to be diagnosed and treated promptly.
Whichever type it is, finding it at an early stage leads to much better treatment results, so it is important to keep watching your own skin and moles.
Skin cancer warning signs: the ABCDE rule
The ABCDE rule is a simple guide for checking whether a mole or spot on the skin could be skin cancer. If your mole matches any one of the following, you should consult a dermatologist:
A – Asymmetry: The shape is not symmetrical (one half of the mole does not match the other half).
B – Border: The edge is uneven, rough or poorly defined.
C – Color: The color is not uniform, with several shades within a single mole.
D – Diameter: It is larger than 6 mm (about the size of a pencil eraser).
E – Evolving: It changes over time, for example in size, shape, color or symptoms (itching, bleeding).
If a mole or spot on your skin shows these signs, see a doctor promptly, because early diagnosis is the key to treating skin cancer.
Skin cancer treatment
Treatment depends on the type and stage of the disease. A specialist doctor will assess you and plan the treatment that suits you:
BCC / SCC: Mohs surgery is the gold standard of treatment. The tissue is removed and examined layer by layer so that as much normal tissue as possible is preserved. It can cure the cancer if it is found early. Standard surgical removal may also be used in some cases.
Melanoma: Surgery is the main treatment while the cancer has not spread. For advanced cases, the doctor may consider immunotherapy (checkpoint inhibitors such as PD-1 inhibitors) and targeted therapy (BRAF inhibitors).
The choice of treatment must always follow a diagnosis by a dermatologist. Do not diagnose or treat yourself.
Prevention and skin care
Although skin cancer cannot be prevented 100%, protecting your skin from the sun helps reduce the risk:
Sunscreen: Apply sunscreen of SPF 30-50 or higher regularly.
Avoid strong sun: Avoid intense sunlight during roughly 10:00 a.m. to 4:00 p.m.
Cover up: Wear long sleeves, a hat and sunglasses when outdoors.
Check your skin: Look over your moles and any unusual spots on your skin at least once a year. If you notice changes according to the ABCDE rule, see a doctor promptly.
Frequently asked questions
Can skin cancer be cured completely? BCC and SCC can be cured if found early, especially with Mohs surgery, which is the gold standard. Melanoma found at an early stage, before it has spread, also has a good chance of successful treatment. Early detection is therefore very important.
What is the ABCDE rule used for? The ABCDE rule is used to check whether a mole or spot on the skin could be skin cancer: A - asymmetrical shape, B - uneven border, C - uneven color, D - larger than 6 mm and E - evolving (changing). If a mole matches any one of these, you should consult a doctor.
What is Mohs surgery? Mohs surgery is an operation in which tissue is removed and examined layer by layer, to remove all of the cancer cells while preserving as much normal tissue as possible. It is the gold standard for treating BCC and SCC, and offers a high chance of cure if the cancer is found early.
When should I see a doctor? See a dermatologist right away if you notice a mole or spot on your skin that fits the ABCDE rule or that is changing, for example growing, changing color, bleeding or forming a sore that does not heal, so that you can get an accurate diagnosis.
If you notice a mole or a skin abnormality that matches the warning signs, do not wait. Consult a dermatologist at Siam Dermatology by calling +66 61 448 7000 or via LINE @siamderm for a thorough examination.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed July 16, 2026
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