Skin Cancer

Skin cancer occurs when cells within the skin begin to grow and divide abnormally, most often as a result of DNA damage caused by ultraviolet (UV) radiation from the sun or tanning beds. The skin is made up of several layers, with the outer layer (the epidermis) containing three main cell types — squamous cells, basal cells, and melanocytes, the pigment-producing cells that give skin its colour. Skin cancer is broadly grouped into two categories based on which of these cells it arises from: non-melanoma skin cancer (which includes basal cell and squamous cell carcinoma) and melanoma, which arises from melanocytes.

These are not simply different names for the same disease — the specific type of skin cancer present has a major bearing on how it behaves, how urgently it needs treatment, and what that treatment involves. Non-melanoma skin cancers are, by far, the most common form of skin cancer overall and are highly treatable, usually growing slowly and rarely spreading elsewhere in the body. Melanoma is far less common but considerably more aggressive, with a much greater tendency to spread (metastasise) to lymph nodes and internal organs if not caught early — which is why understanding the distinction between these types matters so much for how skin changes are assessed and managed.

The Three Main Types of Skin Cancer — And Why the Difference Matters

Understanding which type of skin cancer is present is one of the most important factors in how it is assessed and treated, since the three main types differ significantly in appearance, behaviour and risk.

• Basal Cell Carcinoma (BCC): The most common type of skin cancer, arising from basal cells deep in the epidermis. Typically appears as a pearly or waxy bump, a flat, flesh-coloured or brown scar-like lesion, or a sore that doesn't heal, most often on sun-exposed areas such as the face, neck and scalp. Grows slowly and very rarely spreads to other parts of the body, but can cause significant local tissue damage and disfigurement if left untreated, particularly around the eyes, nose and ears.
• Squamous Cell Carcinoma (SCC): The second most common type, arising from squamous cells in the upper epidermis. Often appears as a firm, red nodule, or a flat lesion with a scaly, crusted surface, commonly on sun-exposed skin including the face, ears, neck, lips and hands. Grows faster than BCC and carries a small but real risk of spreading to nearby lymph nodes if not treated promptly, particularly larger or longstanding lesions.
• Melanoma: The least common but most dangerous type, arising from melanocytes. Often appears as a new dark spot or a mole that changes in colour, size or shape, though a significant minority of melanomas are amelanotic (little or no pigment, appearing pink or skin-coloured, which can make them easy to miss). Melanoma has a considerably higher tendency to spread to lymph nodes and distant organs than the other two types, and outcomes depend heavily on how early it is diagnosed — making early detection especially critical for this type.

Rarer forms of skin cancer, such as Merkel cell carcinoma and dermatofibrosarcoma protuberans, also exist and are managed with specialised, individualised treatment plans given their distinct behaviour.

Recognising Skin Cancer: Symptoms and the ABCDE Rule

The most common warning sign of skin cancer is a change to the skin — either a new growth or a change in an existing mole — and the specific appearance can vary considerably depending on the type involved.

• A pearly, waxy or translucent bump, sometimes with visible small blood vessels
• A firm, red nodule
• A flat, flesh-coloured or brown scar-like lesion
• A flat lesion with a scaly, crusted surface
• A sore that bleeds, oozes, or does not heal within a few weeks
• A mole that changes in colour, size or shape, or that becomes itchy, tender or starts to bleed
• A new, dark spot, or a streak of pigment beneath a fingernail or toenail

For pigmented lesions and moles in particular, the ABCDE rule is a widely used and practical framework for recognising features that warrant assessment.

• Asymmetry: Irregularly shaped moles, where one half doesn't match the other.
• Border: Blurry, notched or irregularly shaped edges, rather than a smooth, well-defined border.
• Colour: A mole containing more than one colour, or uneven distribution of colour, rather than a uniform single shade.
• Diameter: Moles larger than 6 millimetres across (roughly the size of a pencil eraser), although melanoma can occasionally be smaller at diagnosis.
• Evolution: Any mole that is changing — in size, shape, colour, elevation, or in a new symptom such as bleeding or itching. This is widely regarded as the single most important sign to watch for, as change over time is often more telling than any single static feature.

What Causes Skin Cancer

The overwhelming majority of skin cancers are caused by damage to the DNA of skin cells from ultraviolet radiation, which disrupts the normal process by which old skin cells die and are replaced, allowing damaged cells to instead multiply uncontrollably.

• Ultraviolet (UV) radiation from the sun: The primary driver of nearly all skin cancer. UVB rays primarily damage the outer skin layers and are strongly linked to non-melanoma skin cancer, while UVA rays penetrate more deeply and contribute significantly to skin ageing and melanoma risk. Cumulative sun exposure over a lifetime is particularly relevant for basal and squamous cell carcinoma, while intense, intermittent sun exposure and sunburn — especially in childhood — is particularly linked to melanoma risk.
• Tanning beds and sunlamps: Indoor tanning devices emit concentrated UVA and UVB radiation and are associated with a significantly increased risk of all three main types of skin cancer, particularly when use begins at a younger age.
• Genetic factors: A family or personal history of skin cancer, and having a large number of moles or atypical (dysplastic) moles, are both associated with meaningfully increased risk, reflecting an underlying genetic predisposition in how skin cells respond to UV damage.
• Immune suppression: People who are immunocompromised — including organ transplant recipients on long-term immunosuppressive medication — have a substantially higher risk of developing skin cancer, particularly squamous cell carcinoma, and often develop more aggressive disease.
• Radiation and chemical exposure: Previous radiation treatment, and exposure to certain chemicals such as arsenic, can increase the risk of skin cancer developing in the treated or exposed area, sometimes years later.

Risk Factors for Skin Cancer

While anyone can develop skin cancer, certain characteristics and exposures are associated with meaningfully higher risk.

• Skin type: People with fair skin that freckles or burns easily, light-coloured eyes, and blonde or red hair have less melanin to protect against UV damage and face a higher risk of all types of skin cancer. However, skin cancer can occur in people of any skin tone, and is often diagnosed at a later, more advanced stage in people with darker skin, partly due to lower awareness and a tendency for lesions to appear in less sun-exposed areas such as the palms, soles and under the nails.
• History of sunburn: A history of sunburn, particularly severe or blistering sunburn in childhood or adolescence, is strongly associated with an increased risk of melanoma later in life.
• Excessive sun exposure: Cumulative lifetime UV exposure, whether from occupational, recreational or residential sun exposure, increases risk, particularly for basal and squamous cell carcinoma.
• Living in sunny climates or at high altitude: Higher UV intensity at lower latitudes and higher altitudes means greater cumulative UV exposure over time for residents of these regions.
• Numerous or atypical moles: Having many moles, or moles with atypical features, is associated with a higher risk of melanoma developing, either within an existing mole or as a new lesion elsewhere.
• Family history of skin cancer: Having a first-degree relative with melanoma significantly increases personal risk, reflecting shared genetic and environmental factors.
• A weakened immune system: Conditions or medications that suppress immune function reduce the body's ability to detect and eliminate abnormal skin cells before they progress to cancer.
• Exposure to radiation: Previous radiotherapy, particularly at a young age, increases the long-term risk of skin cancer developing within the treated field.

How Melanoma Is Staged: Breslow Depth and Beyond

Once melanoma is diagnosed, determining its stage is one of the most important steps in planning treatment and understanding prognosis, since melanoma is treated very differently depending on how deep it has grown and whether it has spread.

• Breslow thickness: After a suspicious lesion is removed, a pathologist measures how deeply the melanoma has grown into the skin, from the surface down to its deepest point, measured in millimetres. This single measurement, known as Breslow thickness, is one of the strongest predictors of outcome in melanoma — thinner melanomas (generally under 1mm) carry a considerably better prognosis than thicker ones, and Breslow thickness directly guides how wide a surgical margin is needed and whether further staging investigations, such as a sentinel lymph node biopsy, are recommended.
• Ulceration: Whether the surface of the melanoma is intact or broken down is also assessed by the pathologist, as ulceration is associated with a higher risk of spread and factors into overall staging, independent of thickness alone.
• Sentinel lymph node biopsy: For melanomas beyond a certain thickness, or with other higher-risk features, a procedure to identify and remove the first lymph node(s) a tumour would drain to — the "sentinel" node — may be recommended to check for microscopic spread not detectable on physical examination or imaging alone, which provides important additional staging information.
• Overall staging: Melanoma staging (using the TNM system, similar to many other cancers) combines tumour thickness and ulceration, lymph node involvement, and the presence of distant spread to classify the cancer from stage 0 (confined to the outermost skin layer, sometimes called melanoma in situ) through to stage IV (spread to distant organs) — with treatment and expected outcomes varying considerably across this range.

Non-melanoma skin cancers (BCC and SCC) are also assessed for size, depth and specific high-risk features, but are much less frequently staged using this same formal system, since the large majority are treated successfully with local therapy alone.

How Skin Cancer is Diagnosed

Diagnosis of skin cancer combines visual assessment with tissue sampling to confirm the type and, for melanoma, the stage of any cancer found.

• Skin Examination: A thorough visual examination of the entire skin surface to identify suspicious moles, growths or other changes, often assisted by dermoscopy — a handheld magnifying device that allows closer inspection of pigment patterns and structures not visible to the naked eye.
• Skin Biopsy: The definitive way to diagnose skin cancer, involving removal of some or all of a suspicious lesion for examination under a microscope. The specific technique used (shave, punch or excisional biopsy) depends on the size, location and suspected type of lesion.
• Sentinel Lymph Node Biopsy: Recommended for melanomas with certain higher-risk features, to check whether the cancer has spread to nearby lymph nodes, providing important information for staging and further treatment planning.
• Imaging (CT, MRI or PET Scan): Not required for most early, localised skin cancers, but used in more advanced or higher-stage melanoma to check for spread to lymph nodes or distant organs.
• Genetic and Molecular Testing: Increasingly used in advanced melanoma to test the tumour for specific genetic mutations (such as BRAF), which can identify candidates for targeted drug therapy, discussed further below.

Reducing Your Risk: Sun Protection and Self-Examination

Because UV exposure is the primary driver of nearly all skin cancer, consistent sun protection is the single most effective preventive measure, alongside regular self-examination to catch changes early.

• Use sunscreen daily: Apply a broad-spectrum sunscreen of at least SPF 30 to all exposed skin, reapplying every two hours and after swimming or sweating, even on cloudy days and during Singapore's consistently high year-round UV index.
• Wear protective clothing: Wide-brimmed hats, sunglasses with UV protection, and tightly woven, long-sleeved clothing provide reliable physical protection against UV exposure.
• Seek shade during peak UV hours: UV radiation is strongest in the late morning and early afternoon; seeking shade during these hours meaningfully reduces cumulative sun exposure.
• Avoid tanning beds and deliberate sunbathing: Both are significant, avoidable sources of concentrated UV exposure directly linked to increased skin cancer risk.
• Perform regular skin self-examination: Becoming familiar with the pattern of moles and marks on your own skin makes it easier to notice new growths or changes; checking your skin roughly once a month, including areas that are hard to see such as the back, scalp and soles, using a mirror or asking a partner to help, supports early detection.
• Consider professional skin checks: For those with significant risk factors — fair skin, many moles, a personal or family history of skin cancer — a periodic professional skin examination, sometimes assisted by dermoscopy or whole-body photography, adds an additional layer of early detection beyond self-examination alone.

Sun protection remains important throughout life, but it is worth noting that no amount of prior sun exposure makes future protection pointless — reducing ongoing UV exposure continues to lower skin cancer risk at any age.