Squamous cell carcinoma (SCC) is a type of skin cancer that arises from the uncontrolled growth of abnormal squamous cells. SCCs can develop anywhere on the body but are most commonly found on sun-exposed areas. Some sites are at higher risk than others for developing SCC based on sun exposure patterns, immune surveillance, and other factors. Understanding the highest risk sites for SCC helps guide prevention and early detection efforts.
What is Squamous Cell Carcinoma?
Squamous cells are flat, scale-like epithelial cells found lining organs and body cavities such as the mouth, esophagus, and vagina. SCC arises when DNA damage from UV radiation and other carcinogens causes squamous cells to multiply uncontrollably and form malignant tumors. It begins as a precancerous actinic keratosis lesion that develops into an invasive SCC over time if left untreated.
SCC often appears as a scaly red patch, open sore, or elevated growth. While relatively slow-growing, without treatment SCC can destroy healthy tissue and spread to other parts of the body. Immunosuppressed individuals are at higher risk for aggressive SCCs. SCC accounts for approximately 20% of nonmelanoma skin cancers.
Head and Neck
The head and neck region contains some of the highest risk sites for developing SCC. This area receives intense ultraviolet radiation exposure from the sun. The delicate skin covering the lips, ears, scalp, and neck is particularly vulnerable to sun damage over time.
Specific high-risk sites on the head and neck include:
- Lips – The lower lip in particular receives excess sun and is a common site of actinic cheilitis precancerous lesions.
- Ears – The outer ears have sensitive skin with little protective pigment.
- Eyelids – The skin covering the eyelids is the thinnest on the body.
- Temples and balding scalp – Loss of protective hair exposes these areas to increased UV radiation.
- Nose – The tip and sides of the nose are common SCC sites.
The lips account for over 30% of head and neck SCCs. SCC of the external ear is also very common. Fair-skinned individuals are especially vulnerable to SCCs of the head and neck.
Prevention
Preventing SCC in the head and neck centers around limiting UV exposure by:
- Wearing a wide-brimmed hat and UV-blocking sunglasses outside
- Applying broad spectrum SPF 30+ sunscreen
- Avoiding peak sun hours between 10am-2pm
- Seeking shade when outdoors
These sun-safety practices should start early in childhood due to the cumulative nature of sun damage. Self skin exams to identify any suspicious lesions early are also recommended.
Hands
The hands are the most common site of SCC, accounting for around 35-40% of tumors. The dorsal surface of the hands receives frequent UVA and UVB light exposure while performing outdoor activities.
The dominant hand used for tasks like driving typically has a higher SCC incidence. The right hand is most often affected for right-handed individuals. Chronic sun exposure causes actinic keratoses on the dorsal hands which can progress to invasive SCC.
Occupational sunlight exposure further increases risk. Farmers, construction workers, landscapers, and other outdoor workers are especially prone to developing hand SCCs over time.
Prevention
To minimize SCC risk on the hands:
- Wear sun-protective gloves while working outdoors
- Apply broad spectrum, water resistant sunscreen to exposed hands
- Check hands regularly for any new or changing lesions
Avoiding tanning and using UV protection early in life are key to reducing cumulative sun exposure to the hands over time.
Arms
After the hands, the arms are the second most common anatomical site for SCC tumors. The arms are regularly exposed to the sun while wearing short sleeves or tank tops in warm weather.
Actinic keratoses commonly arise on the forearms and upper back of the arms. These precancerous lesions have the potential to progress to SCC if not treated. The right arm again tends to be more frequently affected than the left.
Outdoor workers like landscapers have elevated rates of arm SCCs since the arms are exposed while wearing short sleeve shirts for work.
Prevention
Protecting the arms from excessive sun exposure helps reduce SCC risk. Preventive methods include:
- Covering arms with long sleeve UV blocking shirts
- Applying broad spectrum sunscreen to exposed arms
- Seeking shade between 10am-2pm when UV rays are strongest
- Wearing wide brim hats to shade the arms
Self skin exams to spot any new or changing lesions on the arms are also recommended.
Face
After decades of sun exposure, the facial skin is also vulnerable to SCC tumors. Fair-skinned individuals are especially at risk since they lack skin pigment to help absorb UV radiation.
The cheeks, nose, forehead, temples, lips, and ears are frequent sites for facial SCCs to arise from precancerous actinic keratoses. SCC around the lips accounts for over 30% of lower face tumors.
Men are disproportionately affected by facial SCCs, likely due to higher cumulative sun exposure over time. Outdoor occupations also increase risk.
Prevention
Preventive measures to reduce SCC risk on the face include:
- Daily broad spectrum sunscreen application
- Seeking shade when possible
- Wearing wide brim hats and sunglasses
- Avoiding indoor tanning
- Checking for new facial lesions regularly
Sun safety practices should start at an early age to reduce a lifetime of sun exposure to the facial skin.
Scalp
The scalp is a high-risk anatomical site for SCC, especially in bald individuals. Male pattern baldness exposes the delicate scalp skin to increased UV radiation.
Statistically, the left side of the scalp has a higher SCC frequency since it receives more UV light exposure while driving. The temple, bald crown, and upper neck are common locations for scalp SCCs.
A history of sunburns, fair skin, and outdoor occupations all elevate risk. Individuals with darker skin tones are less prone to scalp SCCs.
Prevention
Protecting the sensitive scalp skin from sun damage is key to lowering SCC risk. Preventive scalp care includes:
- Wearing wide-brim hats or caps outdoors
- Using broad spectrum sunscreen on exposed scalp
- Staying in the shade when possible
- Conducting self-exams for new scalp lesions
For those with bald spots or thinning hair, vigilant sun protection for the vulnerable scalp is vital.
Ears
The external ears receive significant sun exposure and represent a high-risk site for SCC development. The upper helix and antihelix ridges of the outer ears are especially vulnerable.
Men have a disproportionately higher rate of ear SCCs. Fair-skinned individuals are also at increased risk. A history of actinic keratoses on the ears elevates the likelihood of progression to SCC.
The left ear has a somewhat higher frequency of SCC compared to the right, possibly due to UV light exposure while driving.
Prevention
Protective measures to lower SCC risk for the ears include:
- Wearing wide-brim hats to shade the ears
- Applying broad spectrum sunscreen to exposed ears
- Using UV-blocking ear covers and headphones outdoors
- Conducting self-exams for new ear lesions
Avoiding excess UV exposure through the ears starting at an early age is recommended to reduce lifetime risk.
Forearms
The forearms are a high exposure anatomical location for sunlight while wearing short sleeves. Prolonged UV exposure causes actinic keratoses and SCCs to arise frequently on the forearms.
The right forearm has a slightly higher SCC rate compared to the left, especially in right-handed individuals. Outdoor occupations like farming, construction work, and landscaping increase risk.
The dorsal forearm surface is more often affected than the ventral side. The distal forearm near the wrist and elbow flexures are common sites.
Prevention
Reducing excessive sun exposure to the forearms can help lower SCC risk. Preventive tips include:
- Wearing long sleeve UV protective shirts outdoors
- Applying water resistant broad spectrum sunscreen
- Staying in the shade during peak sun hours
- Self-checking forearms for new lesions regularly
Early detection of actinic keratoses allows for treatment before potential progression to SCC.
Lower Legs
The lower legs are exposed to the sun year-round, making them prone to precancerous and cancerous skin lesions. The sparse hair coverage on legs provides little protective benefit.
Actinic keratoses frequently arise on the shins and calves after years of sun damage. These can advance to SCC tumors if left untreated, especially in fair-skinned individuals.
The right leg is more often affected than the left due to UV light exposure while driving. Outdoor occupations further increase SCC risk on the lower legs.
Prevention
Preventive measures to reduce SCC risk on the lower legs include:
- Applying broad spectrum sunscreen to exposed legs
- Wearing long UV-blocking pants or leg coverings outdoors
- Conducting self skin checks for changing leg lesions
- Seeking shade when possible
A lifetime of sensible leg coverage and sun avoidance helps minimize SCC risk on the lower legs.
Feet
The feet receive significant sun exposure but have the lowest incidence of SCC tumors. The thick plantar skin on the soles of the feet is relatively resistant to UV damage.
However, the dorsal surface of the feet is vulnerable to chronic light exposure. Tops of the feet sunburn easily and often develop actinic keratoses after years of cumulative damage.
Common SCC sites include the dorsal midfoot, toes, and top of the ankle. Fair-skinned individuals have the highest SCC risk on the feet.
Prevention
Reducing UV light exposure to the feet can help lower SCC risk. Preventive tips include:
- Applying sunscreen to exposed feet
- Wearing socks and closed toe shoes outdoors
- Seeking shade while wearing sandals or flip flops
- Self-checking feet for concerning new lesions
Early detection and treatment of precancerous actinic keratoses on the feet is important to avoid progression to SCC.
Conclusions
In summary, the head and neck, hands, arms, and legs are the highest risk anatomical sites for developing SCC tumors. These areas receive intense sun exposure over decades leading to precancerous and cancerous lesions.
Prevention centers around UV protection through clothing, shade, and vigilant sunscreen use. Avoiding excessive sun damage from childhood is ideal to reduce lifetime SCC risk. Self skin exams aid early detection of concerning lesions.
While SCC has a better prognosis than melanoma, it can still destroy local tissue and spread if not treated. Being aware of the common SCC hotspots allows for targeted preventive care and early intervention when lesions arise.