All the cells are autonomous and have the capacities of self-preservation and self-reproduction, in addition to fulfilling specialized functions in the organism, such as transporting oxygen in the case of red blood cells, or defending against pathogens in the case of white blood cells.
Types of skin cells
There are three main types of cells in the upper layer of the skin (called epidermis):
- Squamous cells: these are flat cells in the outer part of the epidermis that detach constantly as the new cells form.
- Basal cells: these cells are in the lower part of the epidermis, called the basal cell layer. These cells are constantly dividing to replace the squamous cells that are detached from the surface of the skin. As these cells move towards the epidermis they become flattered, and over time they become squamous cells.
- Melanocytes: These cells produce the brown pigment called melanin that causes the skin to tan or brown. Melanin acts as a natural sunblock for the body that protects the deeper layers of the skin against some of the harmful effects of the sun. For most people, when the skin is exposed to the sun, the melanocytes produce more pigment, causing the skin to become tanned or darker.
The epidermis is separated from the deeper layers of the skin by the basement membrane. When skin cancer becomes more advanced, it usually passes through this barrier and deeper layers.
Types of skin cancer
Basal cell carcinoma: It is the most common type of skin cancer. About eight out of ten cases of skin cancer are basal cell carcinomas (also called basal cell cancers). When viewed with a microscope, the cells in these cancers look like cells in the lowermost layer of the epidermis, called the basal cell layer.
Usually, these cancers arise in areas exposed to the sun, especially the head and neck. These cancers tend to grow slowly. It is very rare for basal cell cancer to spread to other parts of the body. However, if a basal cell cancer is left untreated, it can spread to nearby areas and affect the bones, as well as other tissues under the skin.
If it is not removed completely, the basal cell carcinoma can recur (reappear) in the same place on the skin. People who have had basal cell skin cancers are also more likely to develop new cancers elsewhere.
Squamous cell carcinoma.
Squamous Cell CarcinomaAbout two out of ten cases of skin cancer are squamous cell carcinomas (also called squamous cell cancers). The cells in these cancers look like abnormal versions of the squamous cells seen in the outer layers of the skin.
These cancers commonly appear in areas of the body exposed to the sun, such as the face, ears, lips, and the back of the hands. It can also arise in chronic scars or sores on the skin in other parts of the body. Sometimes they start in actinic keratosis (described below). Less frequently, they form on the skin of the genital area.
Squamous cell cancers are more likely to grow into the deeper layers of the skin and spread to other parts of the body than basal cell cancers, although this is still rare.
Keratoacanthomas are dome-shaped tumors that are found on the skin exposed to the sun. They may begin to grow rapidly, although their growth is usually slow. Many keratoacanthomas shrink and even disappear on their own with the passage of time without treatment, but some may continue to grow and some may even spread to other parts of the body. It is often difficult to predict their growth so that many skin cancer experts consider them a type of squamous cell skin cancer and treat them as such.
These skin malignant diseases originate from the melanocytes, the skin cells that produce the pigments. Melanocytes can also form benign (non-cancerous) growths that are known as moles. Melanoma is much less common than basal or squamous cell skin cancers. It is more likely to grow and spread if left untreated. Moles and melanoma are discussed in our document
Actinic keratosis (solar keratosis).
Actinic keratosis tends to grow slowly and usually does not cause any symptoms (although some may cause itching and irritation). Sometimes they disappear on their own, but they can reappear.
Some actinic keratosis can develop into squamous cell skin cancers. Most actinic keratoses do not develop into cancer, although it can sometimes be difficult to differentiate them from true skin cancers. Therefore, doctors often recommend treatment. If they are not treated, you and your doctor should examine them regularly to identify changes that could be signs of skin cancer.
Bowen’s disease manifests as reddish patches. When compared to actinic keratosis, Bowen’s disease spots are usually larger (sometimes more than 1/2 inch wide), more intense red, more scaly and sometimes rough. Like actinic keratosis, Bowen’s disease usually does not cause symptoms, although it can cause itching and irritation.
Like most skin cancers (and actinic keratosis), these spots appear more frequently in areas exposed to the sun. Bowen’s disease can also occur in the skin of the anal and genital areas (where it is known as Queyrat erythroplakia or Bowenoid papulosis). It is often related to a sexually transmitted infection with human papillomavirus (HPV) that can also cause genital warts.
Sometimes, Bowen’s disease progresses to invasive squamous cell cancer so doctors usually recommend treatment. People who have this condition also have an increased risk of suffering from other skin cancers so that follow-up care is important.
Benign tumors of the skin.
Most types of moles (for information on moles read Skin cancer of the melanoma type).
Seborrheic keratosis: patches with relief, brown, brown or black with a waxy texture. Sometimes with a slightly rough surface and which breaks when they are in the legs (also known as stucco keratosis)
Hemangiomas: benign growths of blood vessels, often called strawberry spots
Lipomas: soft tumors composed of adipose cells
Warts: rough surface growths caused by some types of human papillomavirus (HPV).