Squamous Cell Carcinoma (Skin)

What is squamous cell carcinoma?

The epidermis is built mostly from keratinocytes, also called squamous cells. When ultraviolet (UV) light and other factors damage their DNA, they can multiply out of control. SCC develops in stages:

1. Actinic keratosis: rough, scaly precancerous spots on sun-damaged skin. A small fraction progress to SCC.
2. SCC in situ (Bowen's disease): cancer cells through the full thickness of the epidermis but not below it.
3. Invasive SCC: cancer cells have grown into the dermis, from where they can, uncommonly, reach nerves, lymph nodes or distant organs.

On the lips, the precancerous stage is called actinic cheilitis. Squamous cell carcinomas also occur in the mouth, throat, lung, esophagus, cervix and anus; those are different cancers with different treatment. This page covers SCC of the skin.

What does squamous cell carcinoma look like?

• A rough, scaly red or pink patch that may bleed if scratched
• A firm, raised, dome-shaped bump, sometimes with a central crater filled with keratin (a keratoacanthoma-type SCC that can grow fast over weeks)
• A wart-like growth with a crusted surface
• An open sore that heals partly, then breaks down again
• A thickened, scaly or cracked area on the lower lip
• Lesions on the scalp, ears, face, backs of hands, forearms and lower legs (common in women)

SCC can be tender or painful, especially as it grows. In darker skin, SCC is less common but more often appears on sites not exposed to the sun, such as the legs or genitals, or in scars, and is frequently diagnosed later.

Squamous cell carcinoma vs other skin cancers

Causes and risk factors

• Cumulative UV exposure from the sun or tanning beds; outdoor work and living in sunny climates
• Fair skin that burns easily, light eyes and hair
• Age over 50, and male sex
• Many actinic keratoses or a previous skin cancer
• Weakened immune system: organ transplant recipients have a many-fold higher risk, often with multiple aggressive SCCs; also chronic lymphocytic leukemia and HIV
• Human papillomavirus (HPV), particularly in genital and periungual (around the nail) SCC
• Chronic wounds, scars and burns: an SCC in an old scar is sometimes called a Marjolin ulcer
• Radiation therapy, arsenic exposure, and long-term use of certain medicines such as voriconazole
• Genetic conditions such as xeroderma pigmentosum and albinism

High-risk features

Most SCCs are low risk. Doctors classify a tumor as high risk if it has features such as:

• Size over 2 cm, or any size on the ear, lip, eyelid, nose or genitals
• Rapid growth, poorly defined borders, or recurrence after treatment
• Deep invasion (beyond the subcutaneous fat) or thickness over about 6 mm
• Poorly differentiated cells on biopsy
• Perineural invasion: growth along nerves, which can cause numbness or tingling
• Arising in a scar, chronic wound or previously irradiated skin
• Occurring in an immunosuppressed person

High-risk tumors have a higher chance of recurrence and spread to lymph nodes, and may need imaging, wider surgery or radiation.

How it is diagnosed

1. Skin exam and dermatoscopy.
2. Skin biopsy: a shave or punch biopsy confirms SCC and shows how deep and aggressive it is.
3. Lymph node exam: feeling the nodes in the neck, armpit or groin near the tumor.
4. Imaging (ultrasound, CT, MRI or PET-CT) for high-risk tumors, suspected nerve involvement, or enlarged nodes.

Treatment

Low-risk SCC

• Surgical excision: removing the tumor with a margin of normal skin, typically 4 to 6 mm, and checking the edges under a microscope. Cure rates are high.
• Curettage and electrodesiccation: scraping and cauterizing; for small, low-risk tumors on the trunk and limbs.
• For SCC in situ only: topical 5-fluorouracil or imiquimod cream, photodynamic therapy or cryotherapy.

High-risk SCC

• Mohs micrographic surgery: the surgeon removes thin layers and examines 100% of the margin while you wait, repeating until clear. It gives the highest cure rate and spares the most healthy tissue, especially on the face.
• Radiation therapy: after surgery when there is nerve involvement or other high-risk features, or as main treatment when surgery is not possible.

Advanced SCC

When SCC has spread to lymph nodes or other organs, or cannot be removed:

• Surgery to remove affected lymph nodes, often with radiation
• Immunotherapy with PD-1 inhibitors, including cemiplimab and pembrolizumab, which produce lasting responses in many patients
• EGFR-targeted therapy or chemotherapy when immunotherapy is not suitable

Transplant recipients need careful discussion before immunotherapy because it can trigger organ rejection.

Outlook and follow-up

Most cutaneous SCCs are cured by the first treatment. Spread is uncommon overall but more likely with high-risk features. After one SCC, the chance of developing another skin cancer within 5 years is substantial, so follow-up skin checks, usually every 6 to 12 months (more often if high risk), are recommended for life. Learn to examine your own skin monthly.

Prevention

• Seek shade between 10 a.m. and 4 p.m., and wear hats, sunglasses and UV-protective clothing
• Use broad-spectrum sunscreen SPF 30 or higher on exposed skin daily, and lip balm with SPF
• Avoid tanning beds
• Treat actinic keratoses, which lowers the number that progress
• For high-risk people, dermatologists may recommend oral nicotinamide (vitamin B3), which reduces new skin cancers in people with many previous ones, or other preventive medicines for transplant recipients

Frequently asked questions

What does squamous cell carcinoma look like?

It often looks like a rough, scaly red patch, a firm pink or skin-colored bump with a crusted surface, a wart-like growth, or an open sore that bleeds and does not fully heal. It is most common on the face, ears, scalp, lips, hands and forearms.

Is squamous cell carcinoma dangerous?

Most cases are not dangerous when treated early, and cure rates are very high. A small proportion, particularly large, deep or neglected tumors, tumors on the ear or lip, or those in people with weakened immunity, can spread to lymph nodes and be life-threatening.

How fast does squamous cell carcinoma grow?

It usually grows over weeks to months, faster than basal cell carcinoma. Some types, like keratoacanthoma-type SCC, can double in size within a few weeks. Any skin lesion that grows quickly or does not heal within about a month should be checked.

What is the difference between squamous cell and basal cell carcinoma?

Both are common skin cancers linked to sun exposure. Basal cell carcinoma grows slowly, often looks pearly or shiny, and almost never spreads. Squamous cell carcinoma tends to be scaly or crusted, grows faster, and has a small but real risk of spreading.

Can squamous cell carcinoma come back after treatment?

Yes, it can return at the same site, especially if the first tumor was high risk or not fully removed. People who have had one SCC also often develop new skin cancers elsewhere. Regular skin checks and sun protection are important for life.