Skin cancer is the most common of all human cancers, with 1 million people in the U.S. diagnosed each year with some type of the disease.

Cancer occurs when normal cells undergo a transformation and grow and multiply without normal controls. Here are the cancer basics:

• As the cells multiply, they form a mass called a tumor.
• Tumors are cancerous only if they are malignant. This means that they encroach on and invade neighboring tissues (especially lymph nodes) because of their uncontrolled growth.
• Tumors may also travel to remote organs via the bloodstream. This process of invading and spreading to other organs is called metastasis.
• Tumors overwhelm surrounding tissues by invading their space and taking the oxygen and nutrients they need to survive and function.

There are three major types of skin cancers: basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma. The first two skin cancers are grouped together as non-melanoma skin cancers. Other unusual types of skin cancer include Merkel cell tumors and dermatofibrosarcoma protruberans.