Skin cancer is a malignant growth on the skin which can have many causes. The most common skin cancers are basal cell cancer, squamous cell cancer, and melanoma. Skin cancer generally develops in the epidermis (the outermost layer of skin), so a tumor is usually clearly visible. This makes most skin cancers detectable in the early stages. There are three common and likely types of skin cancer, each of which is named after the type of skin cell from which it arises. Unlike many other cancers, including those originating in the lung, pancreas, and stomach, only a small minority of those afflicted will actually die of the disease. Skin cancer represents the most commonly diagnosed cancer, surpassing lung, breasts, colorectal and prostate cancer. Melanoma is less common than basal cell carcinoma and squamous cell carcinoma, but it is the most serious—for example, in the UK there are 9,500 new cases of melanoma each year, and 2,300 deaths. It is the most common cancer in the young population (20 – 39 age group). It is estimated that approximately 85% of cases are caused by too much sun. Non-melanoma skin cancers are the most common skin cancers. The majority of these are called basal cell carcinomas. These are usually localized growths caused by excessive cumulative exposure to the sun and do not tend to spread.
Classification
The three most common types of skin cancers are:
- Basal cell carcinoma
- Squamous cell carcinoma
- Malignant melanoma
Basal cell carcinomas (BCC) is the most common. They are present on sun-exposed areas of the skin, especially the face. They rarely metastasize, and rarely cause death. They are easily treated with surgery or radiation. Squamous cell carcinomas (SCC) are common, but much less common than basal cell cancers. They metastasize more frequently than BCCs. Even then, the metastasis rate is quite low, with the exception of SCCs of the lip, ear, and in immunosuppressed patients. Melanomas are the least frequent of the 3 common skin cancers. They frequently metastasize, and are deadly once spread.
Less common skin cancers include: Dermatofibrosarcoma protuberans, Merkel cell carcinoma, Kaposi's sarcoma, keratoacanthoma, spindle cell tumors, sebaceous carcinomas, microcystic adnexal carcinoma, Pagets's disease of the breast, atypical fibroxanthoma, leimyosarcoma, and angiosarcoma
The BCC and the SCC often carry a UV-signature mutation indicating that these cancers are caused by UV-B radiation via the direct DNA damage. However the malignant melanoma is predominantly caused by UV-A radiation via the indirect DNA damage. The indirect DNA damage is caused by free radicals and reactive oxygen species. Research indicates that the absorption of three sunscreen ingredients into the skin, combined with a 60-minute exposure to UV, leads to an increase of free radicals in the skin, if applied in too little quantities and too infrequently. However, the researchers add that newer creams often do not contain these specific compounds, and that the combination of other ingredients tends to retain the compounds on the surface of the skin. They also add the frequent re-application reduces the risk of radical formation.
Skin cancer as a group
The three main types of cancer are not similar and basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and malignant melanoma cannot be viewed as skin cancer.
- the mechanism that generates the first two forms is different from the mechanism that generates the melanoma. The direct DNA damage is responsible for BCC and SCC while the indirect DNA damage causes melanoma.
- the mortality rate of BCC and SCC is around 0.3% causing 2000 deaths per year in the US. In comparison the mortality rate of melanoma is 15-20% and it causes 6500 deaths per year.
Even though it is much less common than BCCs and SCCs, malignant melanoma is responsible for 75% of all skin cancer-related deaths.
While sunscreen has been shown to protect against BCC and SCC it may not protect against malignant melanoma. When sunscreen penetrates into the skin it generates reactive chemicals. It has been found that sunscreen use is correlated with malignant melanoma. The lab-experiments and the epidemiological studies suggests that sunscreen use correlates with melanoma incidence. The question that has to be asked is: "Are sunscreen users also the ones with the highest lifetime exposure to ultraviolet lights?" or are sun screens tumor promoters or carcinogens themselves. Logics might suggest that sunscreen users also are the ones most likely to be burned or have been burned by sun light. If it is true that some suncreen induces the formation of skin cancers, the physical sunscreen which are metallic in nature (zinc and titanium) are likely safer and likely to be inert. In the past, most sunscreens were chemical blockers (benzones, etc.).
Signs and symptoms
There are a variety of different skin cancer symptoms. These include changes in the skin that do not heal, ulcering in the skin, discolored skin, and changes in existing moles, such as jagged edges to the mole and enlargement of the mole.
- Basal cell carcinoma usually looks like a raised, smooth, pearly bump on the sun-exposed skin of the head, neck or shoulders. Sometimes small blood vessels can be seen within the tumor. Crusting and bleeding in the center of the tumor frequently develops. It is often mistaken for a sore that does not heal. This form of skin cancer is the least deadly and with proper treatment can be completely eliminated with not so much as a single scar.
- Squamous cell carcinoma is commonly a red, scaling, thickened patch on sun-exposed skin. Ulceration and bleeding may occur. When SCC is not treated, it may develop into a large mass. Squamous cell is the second most common skin cancer. It is dangerous, but not nearly as dangerous as a melanoma.
- Most melanomas are brown to black looking lesions. Warning signs that might indicate a malignant melanoma include change in size, shape, color or elevation of a mole. Other signs are the appearance of a new mole during adulthood or new pain, itching, ulceration or bleeding.
- Merkel cell carcinomas are most often rapidly growing, non-tender red, purple or skin colored bumps that are not painful or itchy. They may be mistaken for a cyst or other type of cancer.
Causes
Skin cancer has many potential causes, these include:
- Studies have shown that smoking tobacco and related products can double the risk of skin cancer.
- Overexposure to UV-radiation may cause skin cancer either via the direct DNA damage or via the indirect DNA damage mechanism. Overexposure (burning) UVA & UVB have both been implicated in causing DNA damage resulting in cancer. Sun strength between 10AM and 4PM is most intense. Natural (sun) & artificial UV exposure (tanning salons) are possibly associated with skin cancer.
- UVB rays primarily affect the epidermis causing sunburns, redness, and blistering of the skin when overexposed. The melanin of the epidermis is activated with UVB just as with UVA; however, the effects are longer lasting with pigmentation continuing over 24 hours.
- Chronic non-healing wounds, especially burns. These are called Marjolin's ulcers based on their appearance, and can develop into squamous cell carcinoma.
- Genetic predisposition, including "Congenital Melanocytic Nevi Syndrome". CMNS is characterized by the presence of "nevi" or moles of varying size that either appear at or within 6 months of birth. Nevi larger than 20 mm (3/4") in size are at higher risk for becoming cancerous.
- Human papilloma virus (HPV) is often associated with squamous cell carcinoma of the genital, anal, oral, pharynx, and fingers. It is believed that the HPV vaccine might help to prevent these cancers as well as cervical cancers.
- Skin cancer is one of the potential dangers of ultraviolet germicidal irradiation.
Diagnosis
Clinical diagnosis is made with visual appearance or with the aid of a dermatoscope. The ABCD guideline is helpful for identifying dysplastic nevus and melanoma. Clinical diagnosis can only be confirmed with a skin biopsy. Most skin biopsies are done under local anesthetic with an injection. A shave biopsy is good for diagnosing basal cell carcinoma, while not as well for squamous cell carcinoma. A punch biopsy is preferred for diagnosing squamous cell carcinoma and melanoma over the shave biopsy technique. Excisional biopsy (where the entire lesion is removed down to the deep dermis and subcutanous fat) is the method of choice for diagnosing melanomas. However, for cosmetic reason and practical reasons, a punch biopsy is often used to initially diagnose many large melanomas or melanomas of cosmetically important anatomic locations (nose, face, eyelids, nails, fingers and toes).
Prevention
Although it is impossible to completely eliminate the possibility of skin cancer, the risk of developing such a cancer can be reduced significantly with the following steps:
- avoid the use of tobacco products.
- reducing overexposure to ultraviolet (UV) radiation, especially in early years
- avoiding sun exposure during the day, especially
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