What causes squamous cell cancer

Overview

Squamous cell carcinoma (SCC) is a common type of skin cancer that arises from the squamous cells, which are flat cells that make up the outer part of the epidermis (the outermost layer of skin). It can also occur in other parts of the body, such as the mouth, lungs, and cervix, where squamous cells are also found. While skin SCC is the most prevalent, the underlying causes often involve genetic mutations triggered by various environmental and lifestyle factors.

Causes of Squamous Cell Carcinoma

1. Ultraviolet (UV) Radiation Exposure

The most significant and well-established cause of squamous cell carcinoma, particularly on the skin, is prolonged and cumulative exposure to ultraviolet (UV) radiation. UV radiation damages the DNA in skin cells. While the body has mechanisms to repair this damage, repeated exposure can overwhelm these repair systems, leading to mutations that cause cells to grow uncontrollably. There are two main sources of UV radiation:

• Sunlight: Chronic exposure to the sun's rays, especially without adequate sun protection, is a primary risk factor. This includes cumulative exposure over a lifetime, particularly for individuals who have spent significant time outdoors (e.g., farmers, construction workers, outdoor enthusiasts).
• Tanning Beds and Sunlamps: Artificial sources of UV radiation, such as tanning beds and sunlamps, emit intense UV rays and significantly increase the risk of developing SCC. Studies have shown that using tanning beds before the age of 30 can dramatically increase the risk of skin cancer later in life.

2. Chemical Exposure

Exposure to certain chemicals can also contribute to the development of SCC. A notable example is arsenic, a heavy metal found in some industrial processes, contaminated water sources, and certain pesticides. Chronic exposure to arsenic, whether through ingestion or skin contact, has been linked to SCC, particularly on the palms of the hands and soles of the feet.

3. Chronic Wounds and Inflammation

Persistent skin injuries, chronic inflammation, or non-healing wounds can transform into squamous cell carcinoma over time. This phenomenon is known as Marjolin's ulcer. Conditions that lead to chronic wounds include:

• Severe burns
• Long-standing skin infections
• Chronic ulcers (e.g., venous stasis ulcers)
• Areas of chronic inflammation, such as in certain autoimmune conditions or chronic skin diseases like discoid lupus erythematosus.

The constant cycle of tissue damage and repair in these areas can promote the development of cancerous mutations.

4. Human Papillomavirus (HPV) Infection

Certain types of HPV are oncogenic, meaning they can cause cancer. High-risk HPV strains are strongly associated with the development of SCC in specific locations:

• Anogenital Region: HPV is a major cause of SCC of the anus, penis, vulva, vagina, and cervix. Persistent infection with certain HPV types can lead to precancerous lesions that eventually develop into invasive SCC.
• Oropharynx: HPV, particularly HPV type 16, is also a significant cause of SCC in the oropharynx (the back of the throat, including the base of the tongue and tonsils). This is often referred to as HPV-related oropharyngeal cancer.

5. Immunosuppression

Individuals with weakened immune systems are at a higher risk of developing SCC. The immune system plays a crucial role in identifying and destroying precancerous and cancerous cells. When the immune system is suppressed, this surveillance function is compromised, allowing damaged cells to proliferate.

Causes of immunosuppression include:

• Organ transplant recipients taking immunosuppressive medications
• Individuals with HIV/AIDS
• People undergoing chemotherapy or long-term corticosteroid therapy

Immunosuppressed individuals, especially those with a history of excessive sun exposure, are prone to developing multiple SCCs.

6. Genetic Predisposition and Other Factors

While not as common as UV exposure, certain genetic conditions can increase susceptibility to skin cancer, including SCC. For example, individuals with albinism or certain rare genetic syndromes have a higher risk.

Other less common factors may include:

• Exposure to radiation therapy
• Certain inherited skin conditions
• Fair skin, light hair, and blue or green eyes (individuals with these traits have less melanin, offering less natural protection against UV radiation).

Understanding these causes is crucial for prevention and early detection strategies. Limiting UV exposure, practicing safe sun habits, avoiding tanning beds, and seeking medical attention for non-healing sores or suspicious skin changes are key measures to reduce the risk of squamous cell carcinoma.