Skin cancer is the most common form of human cancer. More than 50% of all cancers are skin cancers. The incidence of skin cancer is higher than all other cancers combined. Since 1992, there has been a 300% increase in incidence of skin cancer. Nearly half of all Americans and two thirds of all Australians who live to age 65 will develop skin cancer at lease once. The most common warning indication of skin cancer is a change in the appearance of the skin, such as new growth or a sore that will not heal. About 80% of all skin cancers are basal cell carcinomas, about 16% are squamous cell carcinomas and 4% are melanomas.
A number of abnormal but relatively harmless skin growths constitute the early warning signs of skin cancer. These may be precancerous lesions, benign tumours that mask or mimic more serious ones, or malignant tumours that are at the moment just on the topmost layer of the skin. They are important to recognise, because they are a warning sign of potential skin cancer.
Skin in a precancerous state is abnormal but not malignant. The term “precancerous” is used because these abnormal areas of skin are more likely to turn malignant than healthy skin. Precancerous growths are visible to the naked eye, and they look different from normal cells when they are examined under a microscope.
When malignant changes occur in the skin, but haven’t spread beyond the top layer of the skin, they are called early cancers or cancers in situ. A barrier called the basement membrane helps delay invasion by malignant cells deeper into the skin.
The lesions are precancerous because without treatment, a percentage of these lesions develop into Squamous Cell Carcinomas (SCCs), which can be very invasive skin cancers. However, not all SCCs develop from AKs. Although the time of progression from AK to SCC is variable, it is advisable to treat all AKs. The American Academy of Dermatology reports the 40% of cases of SCC begin as AKs.
Basal Cell Carcinoma (BCC) is the most common form of cancer. Basal cells are cells that line the deepest layer of the epidermis. An abnormal growth – a tumour – of this layer is known as BCC.
BCC can usually be diagnosed by examination under a microscope with a simple biopsy and is fairly easy to treat when detected early. However, 5 to 10 percent of BCCs can be resistant to treatment or locally aggressive, eating away at the skin around them, sometimes even into bone and cartilage.
When not treated quickly, they can be difficult to eliminate. Fortunately, however, this is a cancer that has an extremely low rate of metastasis, and although it can result in scars and disfigurement, it is not usually life-threatening.
Squamous cells are cells that compose most of the epidermis. An abnormal growth of these cells is known as SCC. Usually SCCs are slow growing and only spread to other parts of the body if left untreated.
Just above the basal layer of cells is a layer known as a prickle layer derived from the upward movement of basal cells to the outer epidermis. SCC develops from the prickle layer just above the basal layer.
New cells push older cells towards the skin’s surface, the older cells die and are sloughed off. This process is controlled by DNA, the body’s genetic material.
When the DNA is damaged, the rate of new cell supply and old cell die off is not in balance. The orderly pattern is disrupted, causing cells to grow out of control resulting in SCC.
Most damage to the DNA of skin cells results from overexposure to UV radiation from sunlight. The damage is cumulative, so childhood sun exposure contributes to the formation of SCC at a much later age.