Squamous cells are small, flat skin cells in the outer layer of skin. When these cells become cancerous, they typically develop into flat or raised, rounded skin tumors. Sometimes the skin around the tumors gets red and swollen.
Most cases of squamous cell carcinoma occur in people who have spent lots of time in the sun—especially those with fair skin and blue eyes. Some cases develop on skin that has been injured or exposed to cancer-causing agents. This type of squamous cell cancer can develop on:
Scars, burns, and long-lasting ulcers
The legs and body of workers exposed to poisons, harsh chemicals, and agents like tar and soot
Skin affected by genital warts
Red patches of skin covered with white scales, a condition called psoriasis, treated with certain therapies.
People with a weakened immune system are at especially high risk of developing squamous cell cancer. This includes people who:
are HIV positive
have received an organ transplant
Taking immune-suppressing medications.
When it is found early and removed, squamous cell carcinoma causes little skin damage. But if the cancer is not removed when it's small, it can leave a scar. In a small number of cases, the cancer spreads to the lymph nodes and other parts of the body. Squamous cell carcinoma is most likely to spread when it is on the lips, ears, or genitals.