There are 3 common types of cancer, although there are many types of rare skin cancer. The 3 common types – BASAL CELL CARCINOMA (BCC), SQUAMOUS CELL CARCINOMA (SCC) and MALIGNANT MELANOMA (MM) – are all very different in behaviour and who they usually affect.

BCC and SCC usually affect older people. They are often associated with sun exposure, although BCCs may occur in areas of the skin where there is prolonged immune suppression, such as the lower legs when there is long-term venous eczema.

BCCs spread locally but very, very rarely do they spread beyond the point where they arise (they don’t METASTASISE as the medical jargon has it). That doesn’t mean they’re not dangerous, because they are inexorable. They grow and grow to incredible size if not treated, SO GET THEM SEEN EARLY. They may invade bone, and blood vessels, and eat away at the body. There are some shocking examples of what they can do in medical museums. There are different types of BCC – low risk types (superficial and nodular) and high risk types (because their edges are difficult to identify clinically – morphoeic and micronodular). Superficial BCCs can be treated by cream, other types by surgery or radiotherapy, both of which have both advantage and disadvantages.

SCCs can spread from the original site (but also invade locally as BCCs do) and so are more dangerous. They usually spread to local LYMPH GLANDS or NODES; in the case of the leg, those are in the groin, arm (armpit, aka AXILLA), head (neck). It is more common for people to die from SCC although it is still rare in the UK.

MM can affect the young as well as the old, and are much more worrying. They can be very difficult for pathologists to identify (the pathologists often say that MM can look like anything. They don’t have to be very advanced to spread; far-flung deposits can show up years after the original lesion has been treated and all-but-forgotten. They made spread to the liver, lungs or anywhere (another old saw of doctors is to ‘beware the patient with the false eye and the big liver) because an MM of the eye (yes, it can occur in the eye) treated by its removal may result in liver deposits years later.

Moles and Malignant Melanoma

MELANOCYTES are funny things. They sit in the bottom layer of the EPIDERMIS (which is the outer covering of the skin; the rest of the skin is the DERMIS) and their job is to make melanin, which they pass onto the cells on either side of them. Melanin protects cells from damage to their DNA by UV light. DNA damage can lead to cancer. People with pigmented skin do not have more melanocytes, just more melanin.

They make moles that are benign and evolve from purely intraepidermial (‘junctional’) to mix epidermal and dermal (‘compound’) and eventually purely (‘intradermal’). ie they move downwards. They may be disfiguring, or become inflamed, or be a nuisance, but they are BENIGN, although they may become malignant.

Dysplastic naevi are not entirely benign and may progress to cancer; therefore, they need to be excised completely and with a sufficient margin of normal tissue.

Melonoma (with or without the prefix ‘malignant’) is NEVER benign. Once diagnosed and excised, it is the job of the pathologist to tell the dermatologist all the technical factors which influence how it will behave and therefore what further treatment is required. The most important thing the pathological assesses is how thick the melanoma is: less than 1 millimetre (see how thin that is?) 1-2 millimetres thick, 2-3 millimetres thick, 3-4 millimetres thick or over 4 millimetres thick. The thicker they are, the worse it is.

Further treatment may include a wider local excision (WLE) of up to 3cm around the original melanoma to mop up any satellite deposits. That’s a lot, believe me.

Melanomas can spread, but they may spread in a funny way. The most usual is to the local lymph glands (or nodes). Sentinel node biopsy is a way of determining if the local nodes are involved or not. Melanoma may spread to the liver or lungs or anywhere, though. Also melanoma may occur in funny locations that never see the sun.

All cancers have abnormal genes. Some melanomas have BRAF mutations that may be used as a therapeutic target – ie if the mutation is present, certain drugs may be of help.

Lastly, people can occasionally live a long time with melanoma that has spread. Usually, though it is an aggressive cancer that kills quite quickly.