Why Is Chemoprevention Necessary for Oral Cancer?
Chemopreventive agents are drugs or natural products used to prevent cancer occurrence. These preventive agents counteract the risk factors of oral cancer. The ideal agent for chemoprevention should have the following characteristics.
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The agent must be easy to administer.
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It should cause little to no toxicity.
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It should have no long-term adverse sequelae or side effects.
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It should also be reasonably affordable for cancer patients.
Ideally, the chemopreventive agent acts best when administered for a short time. While primary chemoprevention aims at premalignant (occurring before cancer) lesions, secondary chemoprevention intends to stop the cancer progression in the oral cavity. Hence, various promising chemopreventive agents are focused on preventing the spread of pre-cancer and cancer in the oral cavity.
What Are the Various Chemopreventive Therapies for Oral Cancer?
Promising agents for the chemoprevention of oral cancer are listed below.
A. Retinoids: Research shows retinoids (chemically derived compounds from vitamin A) as potential chemopreventive agents against oral cancer. However, their mechanism of action for cancer prevention is unclear and currently under investigation. It has been postulated that retinoids possibly act against the proliferation (multiplication) of cancer cells. Further, they may also cause apoptosis (programmed cell death).
B. Beta-Carotene: Nutrition studies have elaborated evidence to demonstrate that the serum levels of beta-carotene (a precursor of vitamin A) are lower in oral cancer patients compared to normal individuals. Beta-carotene is found commonly in green leafy vegetables and yellow and orange fruits. It is also available in tablet or supplement form prescribed by a registered dietician or nutritionist.
One must note that the precursor of beta-carotene may not be converted to vitamin A in some individuals predisposed to oral cancer. According to the latest research, several studies have also implicated lower blood levels of beta-carotene in head and neck cancer patients compared to patients who do not develop these cancers. These findings lead to the hypothesis that beta-carotene deficiency can predispose individuals to cancer cell formation and further proliferation. The mechanism of action of beta-carotene as a chemopreventive agent is hypothesized as an antioxidant effect against free radicals (free radicals can cause cell damage and lead to cancer).
C. N-Acetylcysteine: N-Acetylcysteine (NAC) is an antioxidant compound and a free-radical scavenger in the body. It is considered one of the most encouraging chemopreventive agents. The chemopreventive activity of this compound has been demonstrated even in lung and tracheal cancers in animal models. In rat lung cell studies, the oral administration of NAC completely prevented various deoxyribonucleic acid (DNA) alterations. In addition, it also suppressed cancer development in rodents. Thus, numerous studies indicate that N-acetylcysteine can prevent mutation and cancer through various mechanisms. NAC suppresses cancer cell growth and increases the expression of proteins involved in inhibiting oral cancer. Similarly, it can be used as a chemopreventive agent for oral cancer.
D. Nonsteroidal Anti-inflammatory Drugs: As inflammation has a pivotal role in oral cancer, Nonsteroidal Anti-inflammatory Drugs (NSAIDs) have shown high levels of chemopreventive activity. Research is ongoing to establish the potency of NSAIDs as inhibitors of cancer cell proliferation and chemoprevention. However, NSAIDs can prevent several types of cancer (lung, oral, and pharyngeal) but can also increase the risk of cardiovascular (heart-related) complications and cause various side effects.
E. Vaccines: Human papillomavirus (HPV) related disease is a significant health problem in developed and developing countries. HPV can infect the mouth and cause cancers of the oropharynx (back of the throat, the base of the tongue, and tonsils). Research shows that HPV causes 70 percent of oral cancers in the United States. Therefore, HPV-associated head and neck cancers are increasingly common in the West, but the incidence is unknown in India. Though most people consider vaccines to prevent infectious diseases, they can also prevent cancer of the head and neck caused by HPV. Hence, the vaccine for HPV infection can be useful in preventing oral cancer.
F. Vitamin E: Epidemiologic studies have noted the inverse relationship between serum vitamin E levels and oral cancer. The mechanism of action of vitamin E has been postulated as an effective antioxidant agent in preventing oral cancers. Dietary vitamin E can prevent oral cancer at a premalignant lesion stage. Its actions include boosting immunity, free radical inhibition, membrane integrity, inhibiting cancer cell growth, and cancer cell killing. Various studies suggest the antioxidant role of vitamin E in the treatment of oral premalignant lesions such as oral leukoplakia (a white patch in the oral cavity), oral lichen planus (a white lacy patch in the oral cavity), and oral submucous fibrosis (a disease characterized by a reduction in mouth opening). Vitamin E also improves the effects of cancer chemotherapy and reduces the side effects of chemotherapy and radiation therapy for cancer patients.
G. Interferon therapy: Interferons (immune proteins) are probable anti-cancer agents owing to their additive anticancer mechanism exerted in combination with retinoids.
H. Curcumin: Curcumin is the primary component of turmeric used in preparing Indian dishes and curries. Curcumin has been demonstrated through nutrition research to inhibit the cancer process. Studies in animal oral cancer models suggest curcumin as a safe and non-toxic chemopreventive agent. However, further research is needed to explore the anti-cancer mechanism of curcumin.
Conclusion
Despite global advances in oral cancer treatment, the survival rates of patients have not improved over the last decade due to several risk factors (smoking, betel nut chewing, and alcohol addiction) for developing oral cancer. It is essential to consider the promising research in detecting and preventing oral cancer at an early stage. Moreover, dental surgeons and oral physicians should also emphasize oral health awareness and education programs to elaborate on the risk factors for oral cancers.
