Skin is the largest organ in the body and consists of three layers: the epidermis (outer layer), dermis, and subcutaneous tissue. The epidermis includes squamous cells, basal cells, and melanocytes.
Skin cancer is the most common form of cancer in the United States1 and usually begins in sun exposed areas, but can occur anywhere. The most common skin cancers develop in the epidermal cells listed above2. Squamous cell and basal cell skin cancers, often called the non-melanoma skin cancers (NMSC), are by far the most common skin cancers. Basal cell cancers invade local structures but rarely metastasize. Squamous cell cancers sometimes spread to other parts of the body. Melanoma is the most aggressive and invasive skin cancer, but only 2% of skin cancers evolve from melanocytes. Rare types of skin cancer include skin lymphoma, Merkel cell carcinoma, and Kaposi sarcoma.
The incidence of both non-melanoma and melanoma skin cancers has been increasing over the past decades. Each year in the US, over 5.4 million cases of non-melanoma skin cancer are treated in more than 3.3 million people3. According to the World Health Organization4, 2 to 3 million newly-diagnosed non-melanoma skin cancers occur globally each year.
Increased awareness, earlier diagnosis, and better treatment modalities have all contributed to improved prognoses in all types of skin cancers.
- Rogers HW, Weinstock MA, Feldman SR, Coldiron BM (2015). Incidence estimate of nonmelanoma skin cancer (keratinocyte carcinomas) in the US population, 2012. JAMA Dermatol 151(10):1081-1086.