skin cancer
Meaning of skin cancer: One label covers several different diseases, and which cell a tumor came from matters far more than the fact that it sits in skin.
Definition of skin cancer
Skin cancer is cancer arising in the skin itself, grouped by the cell it starts from. Basal cell and squamous cell carcinoma both begin in the epidermis, the outer layer, and together account for the great majority of cases. Melanoma begins in melanocytes, the pigment-making cells, and is far more likely to spread beyond the skin.
What are the main types?
| Type | Starts in | Behavior |
|---|---|---|
| Basal cell carcinoma | Basal cells at the base of the epidermis | Most common of all; grows locally, rarely spreads |
| Squamous cell carcinoma | Keratinocytes higher in the epidermis | Second most common; can reach lymph nodes, though uncommonly |
| Melanoma | Melanocytes, which make pigment | Fewer cases, but spreads readily and causes most skin cancer deaths |
| Merkel cell carcinoma | Cells resembling Merkel cells, touch sensors at the base of the epidermis | Rare, fast growing, often linked to a common virus and to suppressed immunity |
Merkel cells carry features of both nerve and hormone-producing tissue, which is why this tumor is described as neuroendocrine. The first two types together are called nonmelanoma skin cancer, a grouping that exists mainly to separate them from melanoma.
What raises the risk?
Ultraviolet light dominates, from sunlight and from tanning devices. The pattern differs by type: steady cumulative exposure over decades tracks with basal cell carcinoma and squamous cell carcinoma, while intense intermittent exposure and blistering sunburns track more strongly with melanoma. Fair skin that burns easily, light hair and eyes, many moles or unusual ones, older age, a family history and a previous skin cancer all add to it. A suppressed immune system raises risk sharply, which is why people who have had an organ transplant develop these cancers far more often. Earlier radiation treatment, long-term arsenic exposure and chronic wounds or scars are less common contributors.
Why does the type matter so much?
Because behavior differs by an order of magnitude. A tumor confined to the epidermis that never leaves the skin poses a very different problem from one that seeds lymph nodes early. The type is settled by examining tissue under a microscope, not by appearance alone, and it determines how widely the surrounding skin is assessed, whether nearby lymph nodes are considered, and how the person is followed afterward. Most skin cancers appear on sun-exposed sites, but melanoma in particular can arise on skin that is rarely uncovered, including the soles, palms and nail beds.
Used in a sentence
A changing mole was biopsied to rule out melanoma or another form of skin cancer.
Good to know
Melanoma is far more likely to spread to distant sites than basal cell or squamous cell carcinoma, which is why the type identified on biopsy shapes how the cancer is assessed and followed.