Skin cancer goes by several medical names depending on which type of skin cell becomes cancerous. The three most common are basal cell carcinoma, squamous cell carcinoma, and melanoma. Together, these account for the vast majority of skin cancer diagnoses, though rarer types exist as well.
The Two Main Categories
Doctors divide skin cancer into two broad groups: non-melanoma skin cancers (also called keratinocyte carcinomas) and melanoma. Non-melanoma covers basal cell carcinoma and squamous cell carcinoma, which are far more common and generally less dangerous. Melanoma is less common but more aggressive, making it responsible for most skin cancer deaths.
Basal Cell Carcinoma
Basal cell carcinoma (BCC) is the single most common type of skin cancer. It begins in basal cells, which sit at the bottom of the outermost layer of skin. BCC typically appears as a change in the skin, often a slightly transparent or pearly bump, though it can also look like a flat, scaly patch or a sore that won’t heal.
On lighter skin, BCC often looks like a skin-colored or pink bump. On brown and Black skin, it tends to appear as a brown or glossy black bump with a rolled border. Tiny blood vessels may be visible on the surface. BCC grows slowly and rarely spreads to distant parts of the body, but it can damage surrounding tissue if left untreated.
Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) starts in squamous cells, which make up the middle and outer layers of the skin. It’s the second most common skin cancer. SCC can appear as a firm bump (called a nodule), a flat sore with a scaly crust, or a rough patch on the lip that may develop into an open sore. It can also show up inside the mouth or on the genitals.
The color varies widely. On different skin tones, SCC nodules can look pink, red, brown, or black. Unlike basal cell carcinoma, squamous cell carcinoma carries a higher risk of spreading to lymph nodes or other organs, particularly when it develops on the ears, lips, or on top of old scars.
Actinic Keratosis: The Pre-Cancer Stage
Before squamous cell carcinoma develops, a precancerous lesion called actinic keratosis (AK) often appears first. These are rough, scaly patches caused by years of sun exposure. Not every actinic keratosis becomes cancer, but the risk of developing squamous cell carcinoma runs about 2% per year once you have one or more of these lesions. That’s why dermatologists typically treat them early.
Melanoma
Melanoma develops in melanocytes, the cells that give skin its color. It’s the most dangerous common skin cancer because it spreads more readily to other parts of the body. An estimated 112,000 new melanoma cases will be diagnosed in the U.S. in 2026 alone.
There are four main subtypes of melanoma:
- Superficial spreading melanoma is the most common type. It initially grows along the top layer of skin before penetrating deeper.
- Lentigo maligna melanoma tends to develop on the face, scalp, or neck, usually in older people with significant sun damage.
- Nodular melanoma grows downward into the skin more quickly than other types.
- Acral lentiginous melanoma is the most common form of melanoma in people of African and Asian descent. It develops on the palms, soles of the feet, or under fingernails and toenails, areas that aren’t typically associated with sun exposure.
How to Spot Melanoma: The ABCDE Rule
The National Cancer Institute uses the ABCDE rule to describe the visual warning signs of early melanoma:
- Asymmetry: One half of the mole doesn’t match the other.
- Border: The edges are ragged, notched, or blurred, and pigment may spread into surrounding skin.
- Color: Multiple shades are present, including black, brown, tan, white, gray, red, pink, or blue.
- Diameter: The spot is larger than 6 millimeters (about the size of a pencil eraser), though melanomas can sometimes be smaller.
- Evolving: The mole has changed in size, shape, or color over recent weeks or months.
Rarer Types of Skin Cancer
Merkel cell carcinoma is a rare but aggressive skin cancer that most often appears as a painless, fast-growing bump on the face, head, or neck. It’s also called neuroendocrine carcinoma of the skin. Despite its name, researchers no longer believe it actually starts in Merkel cells (touch-receptor cells in the skin). A common virus called Merkel cell polyomavirus, which normally lives harmlessly on the skin, plays a role in triggering this cancer. Merkel cell carcinoma tends to spread quickly, so early detection matters significantly.
Other rare skin cancers include sebaceous carcinoma, which starts in oil glands (often near the eyelid), and dermatofibrosarcoma protuberans, a slow-growing cancer in the deeper layers of skin.
Terms You May See on a Pathology Report
If you’ve had a biopsy, your report will use specific language to describe how advanced the cancer is. Two key terms to understand:
- In situ means “in place.” The cancer cells are still confined to the outermost layer of skin (the epidermis) and haven’t invaded deeper tissue. This is the earliest stage, sometimes called stage 0 or carcinoma in situ.
- Invasive means the cancer has grown past the epidermis into the deeper layer (the dermis) and surrounding tissue. Invasive cancers generally require more extensive treatment and further testing.
For basal cell and squamous cell cancers of the head and neck, doctors use the TNM staging system. T describes the tumor’s size and depth, N indicates whether cancer has reached nearby lymph nodes, and M notes whether it has spread to distant organs. Stages range from 0 (in situ) to IV (advanced spread). Melanoma has its own staging system based on tumor thickness, ulceration, and whether the cancer has spread.