What is lip cancer?

Lip cancer is a type of oral cancer, and it is the most common oral cancer. It typically affects the lower lip, with over 95% of lip cancers being cancers of the lower lip.¹ Squamous cell carcinomas, which are cancers that develop in the cells of the surface, or outer layer, of the skin, are the most prevalent type of lip cancer. Another form of lip cancer is basal cell carcinomas, which form on the basal or innermost layer of the skin, but this form of lip cancer is rarer and tends to affect the upper lip rather than the lower lip.² However, both these forms of lip cancer have been linked to exposure to UV radiation. Lip cancer more commonly affects individuals who are fair-skinned, and it affects more men than women.² 

Symptoms & diagnosis

Symptoms of lip cancer include open sores in the lip, pain, swelling, bleeding, discolouration and lumps.³ Diagnosing lip cancer will typically involve a physical exam, imaging tests (e.g MRI), and a biopsy.² Because of their visibility, lip cancers are often diagnosed at an early stage, which allows for early treatment before the cancer metastasises and spreads to nearby organs. Early diagnosis and intervention ultimately improve prognosis and increase the survival rate. 

Understanding UV radiation 

Ultraviolet (UV) radiation is a form of electromagnetic energy that is emitted from the sun and other artificial sources used for medical, industrial and cosmetic purposes, such as tanning beds or as a disinfectant.⁴ The three main categories of UV radiation are UVA, UVB, and UVC, which are categorised based on their wavelength, with UVA being the longest wavelength and UVC being the shortest. UVC rays are absorbed by the Earth’s ozone layer, which limits them from reaching Earth’s surface, but are sometimes artificially produced for certain reasons, such as killing germs.⁵ Because UVC rays from the sun are blocked by the ozone layer, humans are not naturally exposed to it, and it is not typically implicated in the development of diseases. Some UVB rays are also absorbed by the ozone layer, but not all rays will be absorbed, and individuals will still be exposed to some UVB rays. UVA rays, however, are not typically absorbed by the Earth’s atmosphere and are often the main form of UV rays that people are exposed to.⁴ 

Moreover, constant exposure to UVA and UVB radiation has been linked to various health issues and diseases, such as sunburn, premature ageing of the skin, and cancer, particularly of the skin and lips. 

The Link between UV radiation and lip cancer

Whilst cancer is often a result of a complex interplay of various factors and does not typically have a singular known cause, prolonged exposure to UV radiation is known to increase the risk of developing lip cancer. This is particularly due to the impact of UV radiation on DNA, as prolonged exposure can cause DNA damage, which can then result in genetic mutations that cause cancer. 

How cancer develops 

In order to understand the role of UV radiation in cancer development, it is important to understand the underlying mechanisms behind cancer and its development. Cancer occurs when there is uncontrollable cell growth and division, which later forms a tumour. This uncontrollable cell growth is caused by genetic mutations, typically affecting tumour-suppressor genes, which can be inherited or, more commonly, arise as a result of DNA damage from carcinogens.⁶ Carcinogens are substances that have been linked to the development of cancer, such as tobacco, alcohol, and UV radiation.

UV Radiation & cancer

In the case of UV radiation, excessive exposure could increase the risk of developing lip cancer as it could damage DNA and cause the mutations that lead to cells uncontrollably growing. UVB rays, in particular, are more implicated in the development of lip cancer and are more carcinogenic in comparison to UVA rays.⁷ UVB rays can penetrate the skin and cause DNA lesions, while also generating molecules known as reactive oxygen species (ROS). This leads to inflammation, oxidative stress and ultimately increases the risk for cancer. Repeated exposure to UVB can cause mutations in tumour-suppressor genes, such as the known p53 gene, which play a major role in regulating cell growth and preventing the formation of tumours.⁸ Mutations in these tumour-suppressor genes can then lead to the development of squamous cell carcinomas and basal cell carcinomas. Although UVB rays tend to play a bigger role in the development of cancer and are more carcinogenic, prolonged exposure to UVA rays can also result in DNA damage and genetic mutations that cause cancer. 

Other Contributing risk factors 

Whilst exposure to UV radiation is one of the primary risk factors for lip cancer, various other factors could play a role in the development of lip cancer. Tobacco is another known carcinogen that has been identified as a major risk factor for the development of lip cancer. Tobacco contains many harmful chemicals that are also carcinogenic, and smoking or chewing tobacco can allow these carcinogens to enter the body and damage the cells lining the lip and mouth. The carcinogens from tobacco interfere with normal cell functions, such as cell death (apoptosis), DNA repair and regulation of the cell cycle. This interference can also cause mutations in significant tumour-suppressor genes, which can cause uncontrollable cell growth and ultimately lead to the development of cancer. Additionally, the carcinogens in tobacco increase oxidative stress by generating free radicals, which are harmful molecules that damage DNA. This combination of DNA damage, oxidative stress, and a weakened immune system caused by tobacco creates an environment where cancer is more likely to develop.⁹ Other risk factors of lip cancer include heavy alcohol use, human papillomavirus (HPV) infections, and a weak immune system.¹⁰ 

Prevention strategies 

Although no cancer is 100% preventable, there are many steps you can take to lower your risk of developing lip cancer. Increasing awareness and making lifestyle changes can significantly reduce one’s risk. Sun protection is extremely important for lowering the risk of not only lip cancer, but also various other forms of skin cancer. Sunscreen contains physical or chemical ingredients that block UV rays, which can protect your skin and lower the risk of lip cancer. Additional measures for sun protection also include wearing protective clothing (e.g hats) and limiting time outside when UV rays from the sun are high.¹¹ Avoiding artificial UV radiation, such as tanning beds, can also protect the skin and lower the risk of lip and skin cancers. Non-UV-related preventative measures include quitting smoking and limiting alcohol use, which can also significantly reduce the risk of developing cancer. 

Summary 

• Lip cancer is the most common oral cancer, and it primarily affects the lower lip. Two of the main forms of lip cancer are squamous cell carcinomas and basal cell carcinomas
• Squamous cell carcinomas, especially, have been linked to prolonged exposure to UV radiation
• UV radiation, especially UVB, is a major risk factor for the development of lip cancer as it can cause DNA damage and promote mutations in tumour-suppressor genes. These mutations can then interfere with cell functions such as cell growth, cell death and the regulation of the cell cycle. Over time, this can cause uncontrollable cell growth and division, which leads to cancer
• Whilst both UVA and UVB rays can be linked to the development of cancer, UVB rays are more carcinogenic and play a bigger role in the development of cancer
• Sun protection can be an effective preventative measure to lower the risk of lip cancer. This includes using sunscreen (especially on the lips), wearing clothing that protects you from the sun, and limiting time outdoors when the UV is high. Additionally, avoiding artificial sources of UV radiation (e.g tanning beds) can also help lower the risk of lip cancer