Squamous cell carcinoma (SCC) is the second most common type of skin cancer, arising from flat cells called keratinocytes that make up the outer layer of your skin. When detected early, the five-year survival rate is 99 percent. It develops when cumulative sun damage triggers genetic changes in these skin cells, causing them to grow uncontrollably and, in some cases, invade deeper tissues.
How SCC Develops in the Skin
Your skin’s outermost layer is built from keratinocytes, cells that produce the protein keratin and form a protective barrier. Ultraviolet radiation from the sun or tanning beds damages the DNA inside these cells, specifically creating errors in a gene called TP53. This gene normally acts as a brake on cell growth, telling damaged cells to stop dividing or self-destruct. Mutations in TP53 appear in over 90 percent of skin cancers diagnosed in the United States, and they show up even in precancerous lesions, meaning this genetic damage is one of the earliest steps in the process.
With each additional UV exposure, the damaged keratinocytes multiply further and accumulate more genetic defects. Over time, this can progress from a precancerous patch to a cancer that breaks through the basement membrane, the thin boundary separating the surface skin from deeper tissue. Once that boundary is crossed, the cancer is considered invasive.
What SCC Looks Like
SCC appears most often on sun-exposed areas: the scalp, ears, backs of the hands, and lips. But it can also develop inside the mouth, on the bottoms of the feet, or on the genitals. The appearance varies, which is part of what makes it tricky to recognize on your own. Common presentations include:
- A firm bump (nodule) that may be skin-colored, pink, red, brown, or black depending on your skin tone
- A flat sore with a scaly crust that may bleed or ooze
- A rough, scaly patch on the lip that can progress to an open sore
- A new sore or raised area developing on an existing scar
- A wartlike growth on or near the genitals or anus
The key warning sign with any of these is change. A spot that grows, bleeds repeatedly, crusts over without healing, or develops a raised border deserves a closer look from a dermatologist.
Precancerous Patches and Progression Risk
Many SCCs start as actinic keratoses, those rough, sandpapery patches that develop on chronically sun-exposed skin. Most actinic keratoses never become cancer. Published estimates for the risk of any single patch progressing to invasive SCC range from 0.025 percent to 16 percent per year, with an average around 8 to 10 percent across studies. The challenge is that doctors cannot reliably predict which individual lesion will progress and which will remain harmless, so most dermatologists recommend treating them proactively.
Who Is Most at Risk
Ultraviolet radiation is the primary risk factor. Skin cancers collectively are the most common cancers in the United States, with over one million cases diagnosed every year, and UV exposure drives the majority of them. The risk is cumulative, meaning decades of everyday sun exposure matter as much as severe sunburns.
People with fair skin that burns easily face the highest risk, but SCC occurs across all skin tones. Other factors that raise your likelihood include a history of tanning bed use, a weakened immune system (from organ transplantation, certain medications, or chronic illness), previous radiation therapy to the skin, and a personal history of any prior skin cancer. Having many actinic keratoses also signals elevated risk.
How SCC Is Diagnosed and Staged
Diagnosis requires a biopsy. A dermatologist removes part or all of the suspicious lesion, and a pathologist examines the tissue under a microscope to confirm whether cancerous cells are present and how deeply they’ve invaded.
If the biopsy confirms SCC, staging determines how serious it is. Small tumors (2 centimeters or less) without aggressive features are classified as early stage. Tumors larger than 2 centimeters, or those with high-risk characteristics, are staged higher regardless of size. High-risk features include poor cellular differentiation (meaning the cells look very abnormal), location on the ear or lip, thickness greater than 2 millimeters, and growth along nerves. More advanced stages involve invasion into bone or deep structures like the eye socket or skull base.
Treatment Options
Most SCCs are caught early and cured with outpatient procedures. The specific approach depends on the tumor’s size, location, and risk level.
Standard Surgical Excision
The surgeon removes the visible cancer along with a margin of surrounding normal-looking skin. The tissue is sent to a lab, where the edges are checked for remaining cancer cells. If the margins are clear, the procedure is complete. One limitation: less than 1 percent of the tissue margins are typically examined with this method, so there’s a small chance cancer cells at the edges could be missed.
Mohs Micrographic Surgery
Mohs is the most precise option, reserved for high-risk SCCs or tumors in cosmetically sensitive areas like the face. The surgeon removes tissue one thin layer at a time, examining 100 percent of the deep and side edges under a microscope before deciding whether to take more. This continues until no cancer cells remain. The result is maximum cancer removal with minimal loss of healthy tissue. It’s typically done in a single visit, though the process can take several hours because of the repeated microscope checks.
Immunotherapy for Advanced Cases
When SCC has spread beyond the skin or can’t be removed with surgery or radiation, immunotherapy becomes an option. These drugs work by blocking a protein that cancer cells use to hide from the immune system, essentially removing the cancer’s camouflage so your body can attack it. Several of these treatments are now approved for advanced SCC, and one can also be used after surgery and radiation in high-risk patients to reduce the chance of recurrence.
Survival Rates and Why Early Detection Matters
The numbers tell a clear story about the value of catching SCC early. When the cancer is still confined to the skin, the five-year survival rate is 99 percent. Once it has spread beyond the skin to lymph nodes or distant organs, that rate drops below 50 percent.
Metastasis is uncommon with SCC overall, but certain features increase the risk: tumors thicker than 2 millimeters, tumors growing along nerves, location on the ear or lip, and having a suppressed immune system. If you’ve had one SCC, your risk of developing another is significantly elevated, making regular skin checks with a dermatologist an ongoing priority rather than a one-time event.