What is Skin Cancer?

What is Skin Cancer?

Skin is the largest organ of the body. It is made up of three main layers: the epidermis (outer layer), the dermis (inner layer), and the hypodermis (the deep fatty layer). Our skin protects us against injury and infection. In addition, it regulates our body temperature, maintains our water and fat storage, and produces Vitamin D. Skin cancer occurs when skin cells grow abnormally.

Types of Skin Cancer


There are three main types of skin cancer:

  • Basal cell carcinoma - The most common type of skin cancer
  • Squamous cell carcinoma - Not usually life-threatening but aggressive and can grow quite large if left untreated. Serious complications are possible if squamous cell carcinoma spreads to lymph nodes or other organs.
  • Melanoma - Considered the most serious of these three skin cancers. It can develop in an existing mole or unexpectedly change the appearance of skin or show up as a dark spot.

Other types of skin cancer include:

  • Merkel cell carcinoma – A very rare type of skin cancer. Risk factors for Merkel cell carcinoma include a weakened immune system and overexposure to the sun. This type of skin cancer usually presents as a painless lump on sun-exposed areas.
  • Dermatofibrosarcoma protuberans (DFSP) – A rare, slow-growing type of skin cancer that forms in the deepest layer of skin called the dermis. Though it rarely spreads to other body areas, it has a high recurrence rate.
  • Kaposi's sarcoma - A rare skin cancer that forms in the cells lining the blood and lymph vessels. The two types of Kaposi's sarcoma are:
    • Classic Kaposi's Sarcoma (CKS) – This type of cancer is mainly seen in men of Eastern European, Middle Eastern, and Mediterranean background. It is a slow-growing cancer that is usually easy to treat with few serious problems.
    • Kaposi's sarcoma – An aggressive skin cancer that affects people with compromised immune systems, cancer patients, organ transplant recipients, and people with HIV. This fast-growing, potentially deadly skin cancer has been declining since the introduction of antiviral drugs.
  • Sebaceous carcinoma - This rare type of skin cancer begins in the oil glands, particularly the eyelids. This skin cancer may appear as a lump or thickening of the skin, especially near the eyelids.
  • Microcystic adnexal carcinoma (MAC) - This rare type of skin cancer presents itself as a tumor that grows in the sweat glands, particularly on the head and neck or areas most exposed to the sun. People 50 years and older are more likely to develop MAC tumors, and though they can be aggressive, they rarely spread to further parts of the body. These types of tumors are usually treated with Mohs surgery.
  • Undifferentiated pleomorphic sarcoma - Rare, soft tissue skin cancer that develops tumors which can occur anywhere on the body. It primarily affects older men and forms in the dermis layer of the skin. These tumors grow quickly and can spread to other parts of the body. They are often surgically removed using Mohs surgery, radiation therapy, chemotherapy, or immunotherapy.
  • Extramammary Paget's disease (EMPD) – A rare, slow-growing cancer which develops in the sweat glands in the armpits, anus, or genitals. It can go unnoticed for years. It is related to Paget's disease of the breast.

Stages of Skin Cancer

The stages of skin cancer can differ depending on the cancer subtype.




  • Stage 0 – Melanoma in situ, as it is called, is the very beginning stage of skin cancer. In stage 0 melanoma in situ, cancerous cells have begun to appear in the epidermis, which is the outermost layer of the skin. However, the cancer has not spread any further.
  • Stage I and Stage II – Stage I and Stage II melanoma are considered invasive cancer that has spread beyond the epidermis to the dermis, the next layer of skin. At this point, the melanoma has not reached the lymph nodes.

    The two key components determine how advanced Stage I and Stage II cancer are: Breslow depth and ulceration. Doctors use the Breslow depth when describing a melanoma's depth in millimeters. It determines how far the melanoma has extended below the skin surface; a thin melanoma is considered more curable.

    Ulceration indicates broken skin over the melanoma and can be so tiny that it can only be viewed under a microscope. Ulceration is a main factor in staging. Melanoma with ulceration requires more extensive treatment than melanoma without ulceration.
  • Stage I-A
    • The depth of the tumor measures 1 millimeter or less according to the Breslow depth
  • Stage I-B
    • According to Breslow depth, the tumor measures 1.1 to 2 millimeters thick without ulceration
  • Stage II-A
    • Breslow depth tumor thickness measure 1.1 to 2 millimeters with ulceration
    • The tumor is 2.1 to 4 millimeters in Breslow depth without ulceration
  • Stage II-B
    • The tumor is between 2.1 to 4 millimeters in Breslow depth thickness with ulceration
    • The tumor is greater than 4 millimeters in Breslow depth without ulceration
  • Stage II-C
    • The tumor measures 4 millimeters or greater in Breslow depth with ulceration
  • Stage III
    • Stage III refers to melanoma that has either spread to nearby lymph nodes or has spread beyond the initial tumor, yet hasn't reached nearby lymph nodes
    • Melanoma that has spread less than 2 millimeters from the primary tumor but has not invaded the lymph nodes is called a satellite melanoma. In-transit melanoma refers to melanoma that is more than 2 millimeters away from the primary tumor but has not reached the lymph nodes.
  • Stage IV
    • Stage IV is the most advanced melanoma. The tumor can be any size, but it has spread beyond the primary tumor to nearby lymph nodes and distant parts of the body such as the liver, lungs, brain, bone, or gastrointestinal tract.
    • Sometimes Stage IV melanoma is the initial diagnosis. Melanoma at this stage may be considered recurrent, returning in either the initial place it developed, lymph nodes, or other distant parts of the body.

  • Stage 0 - Stage 0 basal cell carcinoma (carcinoma in situ) refers to cancer that is present in the epidermis, the upper layer of skin, and has not spread any deeper or to any lymph nodes
  • Stage I - This includes basal cell cancer that is 2 centimeters or smaller and could possibly spread to the dermis. It does not spread to the lymph nodes or distant organs in the body.
  • Stage II - Stage II includes tumors larger than 2 centimeters that may have spread from the epidermis to the dermis; however, it does not invade the muscles or bones. It has not spread outside the skin and does not spread to the lymph nodes or other organs.
  • Stage III - This cancer has spread below the skin and to local lymph nodes (or facial bones) but not to distant organs
  • Stage IV - The cancer can be any size. This cancer may have spread to several lymph nodes or distant organs such as the lungs, brain, or skull base.

  • Stage 0 - Cancer is located on the epidermis and has not traveled to the dermis
  • Stage I - Cancer has spread below the epidermis but has not spread to lymph nodes or other organs
  • Stage II - The cancer has spread to the epidermis or beyond but has not spread to the lymph nodes or healthy tissues. Stage II squamous cell carcinoma could present one or more high-risk traits such as metastasis to the nerves or lower skin layers.
  • Stage III - Cancer has spread into the lymph nodes but has not traveled to other organs
  • Stage IV - The cancer has spread to one or more organs such as the lungs, liver, brain, or other areas of the skin

  • Stage 0 - The cancer is only in the epidermis, the outermost layer of skin and has not traveled to nearby lymph nodes or other organs. This stage is known as carcinoma in situ.
  • Stage I - The cancer is no more than 2 centimeters and has not spread to nearby lymph nodes to other organs
  • Stage II-A
    • The cancer is more than 2 centimeters but less than 5 centimeters
    • The tumor is more than 5 centimeters but has not traveled to nearby lymph nodes or other organs
  • Stage II-B
    • The cancer has spread to nearby tissues such as bones, muscles, or cartilage
    • The cancer has not spread to lymph nodes or other organs
  • Stage III-A
    • The cancer can be any size and may have spread to nearby tissues
    • The cancer has spread to lymph nodes. However, this discovery was made during a biopsy or surgery and was not visible on any imaging tests.
    • The cancer has not spread to other organs
  • Stage III-B
    • The cancer can be any size and has spread to nearby tissue
    • Cancer has spread to nearby lymph nodes and can be viewed on imaging tests and confirmed by a biopsy or surgery
    • The cancer has spread towards a nearby lymph node. This is called in transit metastasis.
    • The cancer has spread to a nearby lymph node
    • The cancer has not spread to other organs or distant sites
  • Stage IV
    • The cancer can be any size and may have spread into nearby tissues
    • The cancer may or may not have spread to the lymph nodes
    • The cancer has spread to lymph nodes and other organs such as the lungs or other areas of the skin

Signs & Symptoms of Skin Cancer


Each type of skin cancer has its own specific irregularities. However, some general skin cancer symptoms include:

  • Smooth, waxy bumps that form on sun-exposed areas such as the face, ears, neck, or back
  • Lesion on the arms, legs, or trunk of the body that are flat, pink, red or brown
  • Areas on the skin that resemble scars
  • Sores that don't heal and have crusty areas with an indentation in the middle of the lesion that sometimes bleeds

What Causes Skin Cancer?


Scientific research has determined that most skin cancers, such as basal cell carcinoma and squamous cell carcinoma, are caused by overexposure to the sun's harmful ultraviolet rays. Long-term exposure to UV rays can alter the skin's DNA, causing mutations to occur with cell division. The mutated new cells change the development of healthy skin cells, eventually making them cancer cells.

Risk Factors

Risk Factors

Certain risk factors may contribute to formation of skin cancer, including:

  • Overexposure to the sun or tanning beds; living in very sunny places
  • Having light skin that burns or freckles easily, although people of color are still at risk for skin cancer
  • Having light-colored or red hair
  • Having blue, gray, or green eyes
  • Having experienced severe sunburns before the age of 20
  • Moles that change in color, size, or shape
  • Age is a factor—older adults experience skin cancer more than younger people
  • Environmental causes such as exposure to radiation or carcinogenic materials
  • A personal or family history of skin cancer



There are preventive things you can do to help avoid getting skin cancer. Some examples of how you can help prevent skin cancer include:

  • Avoid being in the sun between the peak hours of 11:00 am to 2:00 pm
  • Wear broad spectrum (UVA/UVB) and SPF 30 or greater sunblock, even during the winter months
  • Wear protective clothing when spending time in the sun, this includes wearing a hat and sunglasses
  • Avoid tanning beds
Get Care

Trust NewYork-Presbyterian for Skin Cancer Care

If you're concerned that something "just doesn't look right" and suspect you may have skin cancer symptoms, don't wait. Early detection is your best friend when it comes to skin cancer. If left untreated, skin cancer can leave disfiguring scars or even worse, spread to other areas. Make an appointment with one of NewYork-Presbyterian's world-renowned skin care specialists to learn the about our available treatment options.