About Skin Cancer

Your skin is your body’s largest organ and it serves several important functions. Your skin protects your body from heat, injury and infection; stores necessary water and fat; helps maintain body temperature; and makes vitamin D, an essential nutrient.

How Skin Cancer Forms

Skin cancer is a cancer that forms in the tissue of the skin. Cells differ in shape and function in various organs, but all cells reproduce by dividing. The process of normal tissue growth and repair is usually controlled. However, when uncontrolled, abnormal growth results in masses of tissue called tumors, which can be benign (not cancer) or malignant (cancer).

Begin tumors do not spread. Malignant tumors, on the other hand, invade and destroy normal tissue as they grow. Cancer cells also can break away from the tumor and spread (metastasize) through the blood or lymphatic vessels to form additional tumors in other parts of the body.

The skin consists of two main layers:

Epidermis – This outer, top skin layer is where most skin cancers begin. The epidermis contains four types of cells:

  • Squamous cells are the thin flat cells of the outer skin layer. Squamous cell carcinoma is skin cancer that begins in the squamous cells. 
  • Basal cells are round skin cells that lie under the squamous cells, deeper in the skin. Basal cell carcinoma is skin cancer that begins in the basal cells.
  • Merkel cells are among the basal cells in the deepest epidermis layer. These cells are connected to the nerves endings. Merkel cell carcinoma is rare cancer that begins in the Merkel cells.
    Read more about Merkel Cell Carcinoma
  • Melanocytes are scattered among the basal cells and make melanin, the pigment that colors your skin. Melanoma, is a skin cancer type that begins in the melanocytes. 

Dermis – This deeper, skin layer contains blood vessels, lymph vessels, nerves, sweat and oil glands and hair follicles, which are all held in place by a protein called collagen.

  • Other less common non-melanoma skin cancers, including sebaceous carcinoma, atypical firoxanthoma, dermatofibrosarcoma protuberans, and microcystic adnexal carcinoma can be treated by RPCI’s skin cancer team.

Under the dermis lies the subcutis or hypodermis. This layer is not part of the skin, but connects the skin to muscles and bones. It consists of collagen and fat cells that conserve body heat and act as a shock absorber to protect organs from injury.

Risk Factors & Symptoms

Sun exposure appears to be the leading cause of skin cancer, which usually develops on the most sun-exposed areas face — neck and arms. Fair-skinned people develop skin cancer more often than dark-skinned people, but skin cancers may affect everyone.

Risk factors for non-melanoma skin cancers include:

  • Sunlight (ultraviolet radiation or UV) exposure 
  • Tanning 
  • Severe, blistering sunburns
  • Personal history of a previous skin cancer
  • Receiving an organ transplant
  • Family history of skin cancer
  • Fair complexion (including blonde or red hair, blue eyes, skin that freckles or burns easily)
  • Disease that weakens the immune system such lymphoma, leukemia or human immunodeficiency virus (HIV) 
  • Old scars, burns, ulcers or inflamed skin areas
  • Actinic keratosis (AKs) 
  • Gorlin’s Syndrome – Also called basal cell nevus syndrome. May cause many basal cell carcinomas early in life. 
  • Xeroderma pigmentosum – A rare, inherited condition where the skin has an extreme reaction to sunlight and cannot heal well.
  • Radiation therapy
  • Exposure to chemicals like arsenic, coal or industrial tar
  • Smoking or chewing tobacco
  • Human papillomavirus (HPV) – Some HPV types infect the skin and increase risk for skin cancer. 

Indoor Tanning Dangers

Artificial sources of UV radiation, such as sun lamps, tanning beds and booths are more dangerous than sunlight because their UV radiation is stronger. The World Health Organization declared these tanning devices to be a group 1 carcinogen, putting them in the same group as tobacco, asbestos and uranium as a definite cause of cancer. People who use tanning beds have a higher risk for getting skin cancer and they tend to get skin cancer earlier in life.

Symptoms of Non-Melanoma Skin Cancer:

  • A change on the skin (a new lump or growth, change in an old lump or growth, or a sore that doesn’t heal)
  • A red or brown patch that’s rough and scaly
  • Patch or growth may become itchy or tender but usually skin cancer is not painful

Types of Non-Melanoma Skin Cancer

Cutaneous Squamous Cell Carcinoma

Squamous cell carcinoma is the second most common type of skin cancer. Certain high risk squamous cell carcinomas can spread to lymph nodes and other parts of the body. Appearances of squamous cell carcinomas vary and they may present as a scaly, crusted, or ulcerated bump.

Basal Cell Carcinoma

Basal cell carcinoma is the most common skin cancer. They grow slowly and rarely spread to other parts of the body. Basal cell carcinomas are typically slowly enlarging, pink, pearly bumps that bleed easily, but they may also present as slow growing painless ulcers.


Merkel Cell Carcinoma: Rare and Aggressive

Merkel cell carcinoma is a rare, aggressive neuroendocrine cancer that occurs in the skin. These cancers tend to grow quickly and metastasize (spread) even at an early stage, first to nearby lymph nodes and then to distant sites such as the lungs, brain, bones and other organs. 

Merkel cell carcinomas tend to occur as a single painless lump that is:

  • Fast-growing
  • Firm, dome-shaped or raised
  • Red or violet