Cancer starts when cells in the body change (mutate) and grow out of control. To help you understand what happens when you have cancer, it helps to know how your body works normally. Your body is made up of tiny building blocks called cells. Normal cells grow when your body needs them. They die when your body doesn't need them any longer.
Cancer is made up of abnormal cells that grow even though your body doesn’t need them. In most cancers, the abnormal cells grow to form a lump or mass called a tumor. If cancer cells are in the body long enough, they can grow into (invade) nearby tissues. They can even spread to other parts of the body (metastasis).
Skin cancer starts in the cells of the skin. The part of skin with the cancer is often called a lesion. There are several types of skin cancer (carcinoma). Melanoma is the most serious. But there are others that are called nonmelanoma skin cancer. These include:
Basal cell carcinoma
Squamous cell carcinoma
Merkel cell carcinoma
Cutaneous (skin) lymphoma
Basal cell carcinoma and squamous cell carcinoma are by far the most common nonmelanoma skin cancers.
The skin is the largest organ of the body. It protects us from heat, sunlight, injury, and infection. It also stores water and fat, and makes vitamin D. The skin has 3 layers:
The outer layer called the epidermis
The middle layer called the dermis
The inner, deep layer called the hypodermis, or subcutaneous tissue
The epidermis is made of thin, flat cells called squamous cells. Round basal cells are under the squamous cells. The lower part of the epidermis has pigment-producing cells called melanocytes. These cells make the skin darker when exposed to the sun.
The dermis has blood vessels, lymphatic vessels, hair follicles, and glands. Some of these glands make sweat, which helps keep the body cool. Other glands make an oily substance called sebum. Sebum helps keep the skin from getting dry. Sweat and sebum reach the skin's surface through tiny openings called pores. The main role of the dermis is to support the epidermis. It also cushions deeper tissues, allows skin to stretch, and is important in wound healing.
The hypodermis (subcutaneous tissue) and the lowest part of the dermis form a network of collagen and fat cells. This layer conserves heat and helps protect the body's organs from injury.
Basal cell carcinoma, or basal cell cancer, is by far the most common type of skin cancer. It starts in basal cells in the deepest part of the epidermis. It often starts in skin exposed to the sun, like the face, head, neck, arms, and hands. The cancer lesion often looks like small, raised, shiny, or pearly bumps. But it can have a lot of different looks, like crusty, itchy patches or flat white or yellow spots. They tend to grow slowly and rarely spread to other parts of the body.
Nearly all basal cell cancers can be treated and cured. But sometimes they come back after treatment. This type of cancer rarely spreads to other parts of the body, but if not treated it can grow deeper into bone and tissues under the skin. This can cause serious damage to the bone. Having a basal cell carcinoma means you will likely get new ones in other places. It also puts you at higher risk for other types of skin cancer.
Squamous cell carcinoma, or squamous cell cancer, is the second most common type of skin cancer. It starts in the flat squamous cells in the upper part of the epidermis. Like basal cell cancer, it often starts in skin exposed to the sun, such as the face, ears, lips, head, neck, arms, and hands. But it can also start in skin in the genital area, in scars, and in chronic skin sores. Squamous cell cancer lesions often appear as a rough, scaly, wart-like, reddish patch on the skin that tends to grow quickly. But it can have different looks, too.
Squamous cell carcinoma is more likely to grow and spread to other parts of the body than basal cell carcinoma, but this is still rare. Most squamous cell carcinoma is found early enough to be treated and cured.
Merkel cell cancer is a very rare type of skin cancer. Merkel cells are deep within the upper layer of the skin. They're very close to nerve endings and help the skin sense light touch. Merkel cell cancer starts when these cells grow out of control. Merkel cell cancer can be dangerous because it tends to grow quickly. It can be hard to treat if it spreads beyond the skin.
Merkel cell cancer tumors are most often found on sun-exposed areas of skin, such as the head and neck. But they can start anywhere on the body. They usually look like firm, shiny lumps that don't hurt. The lumps may be red, pink, or blue. They tend to grow very quickly.
Cutaneous lymphoma is a type of non-Hodgkin lymphoma, cancer that starts in blood cells called lymphocytes. These are white blood cells that are part of the immune system. They normally fight infection in the body. This type of lymphoma affects the skin (cutaneous). It causes scaly patches or bumps. It's also known as lymphoma of the skin.
Cutaneous lymphoma is usually slow growing. It develops over many years. There are many different sub-types based on what kind of white blood cell the cancer starts in, how the cancer cells look, and proteins found on the cancer cells.
If you have questions about nonmelanoma skin cancer, talk with your healthcare provider. Your healthcare provider can help you understand more about this cancer.