Skin, the body's largest organ, provides protection, regulates temperature, retains water, produces vitamins and hormones and allows sensory perception. Skin consists of three layers; epidermis---the outer layer, dermis---the inner layer and subcutis---the layer of fatty tissue. Skin cancer, the most common type of cancer as reported by the American Cancer Society, usually begins in cells located in the epidermis. Upon diagnosis, doctors assign the cancer a stage based on the location, the size, the thickness, the depth and the degree of spreading.
Stage 1
Skin cancers are classified into two main groups; melanoma cancers and non-melanoma cancers. Melanoma skin cancer, the most dangerous type, according to the Skin Cancer Foundation, begins in the melanocytes---cells in the epidermis that produce the pigment melanin. Non-melanoma skin cancers include basal cell carcinoma, which begins in the basal cells located in the deepest layer of the epidermis, and squamous cell carcinoma, which affects the flat keratinocytes found just under the dead top layer of cells.
Stage 1a melanoma skin cancer describes a tumor less than 1 mm thick, as measured from the upper layer of epidermis, without ulceration and occupies space only in the epidermis or the thin layer found directly under the epidermis known as the papillary dermis.
Stage 1b melanoma tumors remain less than 1 mm thick but may have ulceration or may penetrate deeper into the dermis. A tumor more than 1 mm thick but less than 2 mm thick without ulceration is also classified as stage 1b. Closest lymph node involvement may occur in stage 1b as well.
Stage 1 non-melanoma describes a tumor confined to the epidermis layer and no more than 2 cm wide.
Stage 2
Stage 2a melanoma describes a tumor between 1 and 2 mm thick, with ulceration or between 2 and 4 mm thick without ulceration. A tumor between 2 and 4 mm thick with ulceration or over 4 mm thick without ulceration progresses to a stage 2b classification. Stage 2c tumors are greater than 4 mm thick with ulceration.
Doctors assign non-melanoma tumors greater than 2 cm wide with penetration into the dermis layer of skin to stage 2.
Stage 3
Doctors assign stage 3 to any melanoma tumor with local or regional lymph node involvement. Any small metastases found in the dermis or subcutis layer more than 2 cm from the primary tumor is also classified as stage 3 melanoma.
Stage 3 non-melanoma describes spreading of the tumor to nearby tissues such as cargilage, bone or muscle or lymph nodes.
Stage 4
Stage 4 melanoma describes a tumor metastasized to lymph nodes located far from the original tumor or to internal organs including the liver, brain, bones and gastrointestinal tract.
Similarly, stage 4 non-melanoma also describes a tumor metastasized to other organs, such as distant lymph nodes, brain or lungs.
