Skin cancer is the most common type of cancer among light skinned individuals. It is the commonest cancer in the United States and in Australia. Each year, about one million people are diagnosed with this cancer. In 85 percent of these cases, the skin damage leading to the cancer occurs before an individual is 18.
Every cell in the body has a tightly regulated system that controls its growth, maturity, division and ultimately death. The blueprint of a cell’s function lies within the DNA of the cell. When there is damage to the DNA the cells begin to divide and grow without control. The mass of extra cells may produce a tumor that can be non-malignant or benign or non-cancerous. The tumor may also be cancer.
Skin is the largest organ in the body with numerous functions. It covers the internal organs and protects them from heat and light, injury and infection. The skin also controls body temperature by sweating and perspiration and stores water, fat and vitamin D. The skin is made up of two layers:-
In skin cancer the cancer begins in cells that make up the skin. Skin cancers are named for the type of cells where the cancer starts. There are three types of skin cancers:
Some of the risk factors for skin cancers include:-
Skin cancers are named after the type of cells in the skin that are involved in the beginning of the cancer. The three most common types include:-
This cancer begins in the basal cell layer of the skin. This is common in areas of skin exposed to the sun. The face is the most common place to find basal cell skin cancer.
In people with fair skin, basal cell skin cancer is the most common type of skin cancer. Basal cell skin cancer rarely spreads to other parts of the body. This is a slow-growing, locally invasive, malignant skin cancer affecting the epidermis.
Subtypes of basal cell cancer include:-
This cancer originates in squamous cells. This is the commonest type of skin cancer seen in dark skinned individuals. It is usually found in places that are not exposed to the sun. In fair skinned individuals squamous cell skin cancer usually occurs on parts of the skin that have been in the sun, such as the head, face, ears, and neck.
Squamous cell skin cancer sometimes spreads to other parts of the body. The risk of spread is between 0.5 to 40% depending on the subtype.
These cancers begin in melanocytes or pigment/melanin producing cells. Melanoma can occur on any skin surface – both those areas exposed to the sun as well as those un-exposed. In men, it's often found on the skin on the head, on the neck, or shoulders and the hips. In women melanomas are commonly detected on the skin on the lower legs or on the shoulders and the hips.
This type of skin cancer is rare in people with dark skin. However, when found in dark skinned individuals, melanomas are detected under the finger or toe nails, on palms and soles.
Melanoma is more likely than other skin cancers to spread to other parts of the body. The cancer cells may be found in nearby lymph nodes and spread via lymphatic channels.
There are several subtypes of malignant melanoma. Superficial spreading melanoma, nodular melanoma and lentigo maligna melanomas make up 90% of all diagnosed malignant melanomas.
Other rarer types include Acral lentiginous melanoma, Acral amelanotic malignant melanoma etc.
Superficial spreading malignant melanoma is the most common type of melanoma seen on the trunk or legs and can appear as a new or existing mole. Nodular malignant melanoma appears blue or red and typically occurs as a new mole. Lentigo maligna melanoma is commonly seen on the face.
There are several risk factors that raise the propensity to get skin cancers by manifold. The exact cause why DNA damage occurs and why cancer results from such DNA damage is not known clearly but these risk factors give an idea regarding factors that can be avoided to prevent skin cancers.
The risk factors of skin cancers include:-
One of the major risk factors for skin cancer is exposure to sunlight (UV radiation). This is particularly true for basal cell and squamous cell cancers that occur in exposed parts of the skin.
Sunlight is a source of UV radiation. This UV radiation exposure leads to damage to the DNA of the cells of the skin. DNA damage is the underlying cause of any type of cancer.
Sunlight exposure may be direct or may be indirect. Indirect exposure results from reflected sunrays by sand, water, snow, ice and shiny surfaces like glass etc. The sun exposure is also high at higher elevations, such as in the mountains. The sun's rays can penetrate through clouds, windshields, windows and even light clothing. In the United States skin cancers are more common where the sun is strong e.g. in Texas.
Those with a propensity for severe sunburns and blisters on exposure to sunlight are at a heightened risk of skin cancers. People who burn easily are more likely to have had sunburn as a child. The total amount of sun exposure over a lifetime is a risk factor for skin cancer. Those exposed to the sun excessively during childhood are at greater risk. It is found that most of the sun’s UV radiation exposure occurs before the age of 18 years.
Studies have shown that a tan slightly lowers the risk of sunburn but the risk remains. People who tan little or not at all and burn more when exposed to sun are more at risk of skin cancers.
These are artificial sources of UV radiation that can cause sun damage to the skin and may raise the risk of skin cancers. Health care providers strongly encourage young individuals especially to avoid using sunlamps and tanning booths. The risk is high in users of sunlamps and tanning booths before the age of 30.
Those with a family history of skin cancers are at a raised risk of skin cancers. Melanoma sometimes runs in families. Having two or more close relatives or first degree relatives (parents, siblings or offspring) raises the risk of melanoma. Other types of skin cancer also sometimes run in families. Those with a family history of xeroderma pigmentosum or nevoid basal cell carcinoma syndrome have a skin that is more sensitive to the sun and increases the risk of skin cancer.
Individuals who have had a melanoma before are at a greater risk of getting it again.
Men are more susceptible to both melanoma and non-melanoma skin cancers. Melanomas can be found in younger people but the rates of all types of skin cancer rises with increasing age.
Individuals with fair or pale skin, especially with blonde, red or light-brown hair and blue, green or gray eyes are at a raised risk.
Some diseases and medications such as some antibiotics, hormones, or antidepressants may make the skin more sensitive to sun exposure and raise the risk of skin cancers.
Individuals with a dysplastic nevus are at a raised risk of getting melanoma. This is a type of a mole that looks different from a common mole. It is bigger, and its edges, structure, surface etc. may be different. It may be longer and wider with patches of several colors ranging from shades of pink to dark brown. The surface is smooth, scrappy or pebbly and edges are rough and blurred. A dysplastic nevus is more likely than a common mole to turn into cancer.
Individuals with more than 50 moles on their body are more at risk of melanomas.
Presence of old large scars, ulcers, burn marks and skin inflammations raise the risk of squamous cell cancers and basal cell cancers.
Arsenic exposure raises the risk of basal cell or squamous cell cancers.
Radiation exposure to skin for other cancers may damage the skin to cause cancers.
Those with Actinic keratosis (a flat, scaly growth on the skin in the exposed areas such as face and the backs of the hands) are at a raised risk of squamous cell cancer.
Exposure to human papillomavirus or HPV also raises the risk of squamous cell skin cancer. These HPVs are different from the HPV types that cause cervical cancer in the female reproductive tract.
Skin cancers originate with common symptoms like abnormal growth in the skin, abnormal changes in existing moles and refusal of existing sores and ulcers on the skin to heal.
Most skin cancers can be found early with skin exams. Skin examinations need to be done regularly at home in susceptible individuals (who have more than one risk factor).
Diagnosis includes the following steps:-
Self examination of the skin is an early method by which skin cancers can be detected early. Self examination should be performed at least once a month.
Self examination should be done in front of a full length mirror in a well-lit room. A smaller hand-held mirror can be used to look at areas that are hard to see. All individuals must be aware of the normal appearance of moles, scars and marks over their skin. This would alert them if there is any change in moles, freckles, or marks over the skin.
The first part includes checking face, ears, neck, chest, and abdomen. Women should lift their breasts to check underneath. Thereafter underarms, arms, tops and bottoms of hands, between fingers and under fingernails should be checked. Next the thighs, shins, feet, soles, in between toes and under toenails should be examined. Using a hand held mirror back of the legs, knees, thighs, buttocks, genital area, lower and upper back, back of the neck and ears, scalp etc. need to be checked.
Basal cell cancers and squamous cell cancers are commonly found in areas of skin exposed to the sun but they can occur elsewhere. One should look for patches, or non healing sores, marks, growths and abnormal moles. A normal mole has an even coloring of brown, tan, or black. The size is usually less than a quarter inch (size of a pea) and can be either flat or raised. It can be round or oval.
A mole can be present at birth, or it can appear during childhood or young adulthood. Moles appearing later in life need to be checked.
Moles usually remain the same shape and size and color throughout life. Some moles may also fade away with age. The most important warning sign for melanoma is abnormality in a mole.
Physicians usually look for the ABCDE symptoms to diagnose a melanoma. These include:-
A detailed medical history of sun exposure, sun burns and family history of melanoma and skin cancers is obtained to ascertain the risk of skin cancers.
Local lymph nodes are examined for swelling. Melanomas can spread to other organs via lymphatic channels.
A skin disease specialist or a dermatologist will next use dermoscopy or epiluminescence microscopy [ELM], surface microscopy, or dermatoscopy to see spots on the skin more clearly. This device is essentially a special magnifying lens with a light source that is held near the skin. A thin layer of oil may be used with this instrument. A digital or photographic image of the spot may be taken.
If the spot appears suspicious the dermatologist may prescribe a skin biopsy to confirm the diagnosis of skin cancer. Different methods can be used for a skin biopsy. For a biopsy a small sample of skin is taken and the sample is sent to the lab. A pathologist looks at microscopic preparations of the sample under the microscope.
Biopsies are usually performed under local anaesthesia. There are some common types of skin biopsies. These include a shave biopsy where a thin slice of the tissue is shaved off from the lesion. For a deeper examination a punch biopsy, an incisional or an excisional biopsy may be undertaken.