What is skin Cancer?
Skin cancer begins when cells in the skin start to grow uncontrollably.
There are 3 main types of cells in the top layer of the skin (called the epidermis):
- Squamous cells: These are flat cells in the outer part of the epidermis that are constantly shed as new one’s form underneath to take their place.
- Basal cells: These cells are in the lower part of the epidermis, called the basal cell layer. These cells constantly divide to form new cells to replace the squamous cells that wear off the skin’s surface. As these cells move up in the epidermis, they flatten, eventually becoming squamous cells.
- Melanocytes: These cells make the brown pigment called melanin, which gives the skin its tan or brown color. Melanin acts as the body’s natural sunscreen, protecting the deeper layers of the skin from some of the harmful effects of the sun. For most people, when skin is exposed to the sun, melanocytes make more of the pigment, causing the skin to tan or darken.
The epidermis is separated from the deeper layers of skin by the basement membrane. When a skin cancer becomes more advanced, it generally grows through this barrier and into the deeper layers.
Types of Skin Cancer
Basal cell carcinoma
This the most common type of skin cancer. About 80% skin cancers are basal cell carcinomas (BCC).
These cancers usually develop on sun-exposed areas, especially the head and neck. These cancers tend to grow slowly. It’s very rare for a basal cell cancer to spread to other parts of the body. However, if a basal cell cancer is left untreated, it can grow into nearby areas and invade the bone or other tissues beneath the skin.
If not removed completely, basal cell carcinoma can recur (come back) in the same place on the skin. People who have had basal cell skin cancers are also more likely to get new ones in other places.
Squamous cell carcinoma
About 20% skin cancers are squamous cell carcinomas (SCC). These cancers commonly appear on sun-exposed areas of the body such as the face, ears, neck, lips, and backs of the hands. They can also develop in scars or chronic skin sores elsewhere.
Squamous cell cancers are more likely to grow into deeper layers of skin and spread to other parts of the body than basal cell cancers, although this is still uncommon.
These cancers develop from melanocytes, the pigment-making cells of the skin. Melanocytes can also form benign (non-cancerous) growths called moles. Melanomas are much less common than basal and squamous cell cancers, but they are more likely to grow and spread if left untreated.
Less common types of skin cancer:
- Merkel cell carcinoma
- Kaposi sarcoma
- Cutaneous (skin) lymphoma
- Skin adnexal tumors (tumors that start in hair follicles or skin glands)
- Various types of sarcomas
Together, these types account for less than 1% of all skin cancers.
Pre-cancerous and pre-invasive skin conditions
- Actinic keratosis (solar keratosis)
- Squamous cell carcinoma in situ (Bowen disease)
- Benign skin tumors
- Most types of moles (see Melanoma Skin Cancer for more about moles)
- Seborrheic keratoses
- Warts: rough-surfaced growths caused by some types of human papillomavirus (HPV)
Basal and Squamous Cell Skin Cancer Risk Factors
Several risk factors make a person more likely to get basal cell or squamous cell skin cancer. These factors don’t necessarily apply to some other forms of skin cancer, such as Kaposi sarcoma and skin lymphoma.
Ultraviolet (UV) light exposure
Exposure to ultraviolet (UV) rays is thought to be the major risk factor for most skin cancers. Sunlight is the main source of UV rays. Tanning beds are another source of UV rays.
While UV rays make up only a very small portion of the sun’s rays, they are the main cause of the damaging effects of the sun on the skin. UV rays damage the DNA of skin cells. Skin cancers begin when this damage affects the DNA of genes that control skin cell growth.
Having light-colored skin
Whites have a much higher risk of skin cancer than African Americans or Hispanics. This is because the skin pigment melanin has a protective effect in people with darker skin. Whites with fair (light-colored) skin that freckles or burns easily are at especially high risk.
The risk of getting basal and squamous cell skin cancers rises as people get older. This is probably because of the buildup of sun exposure over time. These cancers are becoming more common in younger people as well, probably because they are spending more time in the sun with their skin exposed.
Men are more likely than women to have basal and squamous cell cancers of the skin. This is thought to be due mainly to getting more sun exposure.
Exposure to certain chemicals
Being exposed to large amounts of arsenic increases the risk of developing skin cancer. Arsenic is an element found naturally in well water in some areas. It’s also used in making some pesticides and in some other industries. Workers exposed to coal tar, paraffin, and certain types of oil may also have an increased risk of skin cancer.
People who have had radiation treatment have a higher risk of developing skin cancer in the area that received the treatment. This is particularly a concern in children who have had radiation treatment for cancer.
Other Risk Factors:
- Previous skin cancer
- Long-term or severe skin inflammation or injury
- Psoriasis treatment
- Xeroderma pigmentosum (XP)
- Basal cell nevus syndrome (also known as nevoid basal cell carcinoma syndrome or Gorlin syndrome)
- Weakened immune system
- Human papillomavirus (HPV) infection
Can basal and squamous cell skin cancers be found early?
It’s important to check all over your skin, preferably once a month. Skin self-exams are best done in a well-lit room in front of a full-length mirror. Use a hand-held mirror for areas that are hard to see, such as the backs of your thighs. Friends and family members can also help you with these exams, especially for those hard-to-see areas, such as your scalp and back.
Be sure to show your doctor any areas that concern you and ask your doctor to look at areas that may be hard for you to see.
Any spots on the skin that are new or changing in size, shape, or color should be seen by a doctor promptly. Any unusual sore, lump, blemish, marking, or change in the way an area of the skin looks or feels may be a sign of skin cancer or a warning that it might occur. The area might become red, swollen, scaly, crusty or begin oozing or bleeding. It may feel itchy, tender, or painful.
Basal cell and squamous cell skin cancers can look like a variety of marks on the skin. The key warning signs are a new growth, a spot or bump that’s getting larger over time, or a sore that doesn’t heal within a few weeks.
Exam by a health care professional
Having regular skin exams is especially important for people who are at high risk of skin cancer, such as people with reduced immunity (for example, those who have had an organ transplant) or people with conditions such as basal cell nevus syndrome (Gorlin syndrome) or xeroderma pigmentosum (XP). Talk to your doctor about how often you should have your skin examined.
Which treatments are used for basal and squamous cell skin cancers?
Based on the type and stage of cancer and other factors, your treatment options may include:
- Other forms of local therapy
- Radiation therapy
- Systemic chemotherapy
- Targeted therapy
Different approaches might be used to treat basal cell carcinoma, squamous cell carcinoma, actinic keratosis, and Bowen disease.
(Other skin cancers, such as melanoma, lymphoma of the skin, Merkel cell carcinoma, Kaposi sarcoma, and other sarcomas are treated differently)
Which doctors treat basal and squamous cell skin cancers?
You might have different types of doctors on your treatment team. Most basal and squamous cell cancers (as well as pre-cancers) are treated by dermatologists – doctors who specialize in treating skin diseases. If the cancer is more advanced, you may be treated by another type of doctor, such as:
A surgical oncologist: a doctor who treats cancer with surgery
A medical oncologist: a doctor who treats cancer with chemotherapy or other medicines
A radiation oncologist: A doctor who treats cancer with radiation therapy