Dr Kirti Raina Cancer is one of the most common causes of morbidity and mortality today, with more than 10 million new cases and more than 6 million deaths each year worldwide. More than 20 million persons around the world live with a diagnosis of cancer, and more than half all cancer cases occur in the developing countries. Cancer is responsible for about 20 per cent of all deaths in high income countries and 10 per cent in low-income countries. It is projected that in coming years, there will be every year 15 million new cancer cases and 10 million cancer deaths. It is estimated that around 43 per cent of cancer deaths are due to tobacco use, unhealthy diets, alcohol consumption, inactive lifestyles and infection. Of these, tobacco use is the world’s most avoidable cause of cancer. In addition to lung cancer, tobacco consumption causes cancer of the oral cavity, pharynx, larynx, oesophagus, stomach, pancreas, liver, kidney, ureter, urinary bladder, uterine cervix and bone marrow. Cancer incidence and survival rates are clearly linked to socioeconomic factors. Tobacco: Tobacco consumption continues to prevail as the most important cancer risk as it alone accounts for millions of cancer deaths annually. The neoplastic diseases caused by smoking include cancers of the lung, oral cavity, pharynx, larynx, esophagus, urinary bladder, renal, pelvis, and pancreas. The relationship between smoking and oral cancer has been established firmly by epidemiological studies. The use of smokeless tobacco (tobacco consumed without combustion) has become prevalent all over the world. Smokeless tobacco is placed inside the oral cavity in contact with the mucous membranes where the nicotine is absorbed to provide the desired effect. Consumption of smokeless tobacco causes mainly oral pre-cancer and cancer. The habit of oral snuff (referred to as snuff-dipping) causes a condition called ‘snuff-dipper’s cancer’ classically described as verrucous carcinoma. Betel quid: Betelm quid chewing with different ingredients is the most common habit in Southeast Asia, especially in the Indian subcontinent. Some of the common forms of these mixtures are Khaini (tobacco and lime), Mishri (burned tobacco), Zarda (boiled tobacco), Gadakhu (tobacco and molasses), and (tobacco, lime and areca) consumed in different parts of India. Studies have shown the association of these products with oral cancer development. and pre-cancer namely leukoplakia, erythroplakia, and oral submucous fibrosis. Alcohol: Alcohol has been implicated in the development of oral cancer. Alcoholic beverages have been considered carcinogenic to humans causing in particular, tumors of the oral cavity, pharynx, larynx, esophagus, and liver; although ethanol has not been proven carcinogenic in animal studies. Alcohol consumption has been shown to act synergistically with tobacco in the increased risk of development of oral cancer. Few studies have managed to do analysis with patients who drink alcohol but are nonsmokers and in patients who smoke but are nondrinkers. In one such study, alcohol has been found to be an independent risk factor for oral leukoplakia in an Indian population. However, similar studies evaluating the oral epithelial dysplasia occurrence in alcohol drinkers who are nonsmokers, found that the role of alcohol in development of oral epithelial dysplasia is crucial only when considered in conjunction with tobacco. Alcohol is shown to increase the permeability of oral mucosa producing an alteration in morphology characterized by epithelial atrophy, which in turn leads to easier penetration of carcinogens into the oral mucosa. The systemic effects of alcohol are mainly due to the hepatic damage. Alcohol addiction leading to cirrhosis and other diseases (e.g., cardiomyopathy, stroke, and dementia) inhibits the detoxification of carcinogenic compounds such as N?nitrosodiethylamine. Diet & Nutrition: The relationship between diet and nutrition to the risk of cancer development has been established by several epidemiological and laboratory studies. More frequent consumption of fruit and vegetables, particularly of carrots, fresh tomatoes, and green peppers were associated with reduced risk of oral and pharyngeal cancer. Food and food groups other than fruits and raw vegetables that have a protective effect are fish, vegetable oil, olive oil, bread, cereals, legumes, protein, fat, fresh meat, chicken, liver, shrimp, lobster and fiber. Certain food groups have been shown to be associated with higher risk of oral cancer namely processed meats, cakes and desserts, butter, eggs, soups, red meat, salted meat, cheese, pulses, polenta, pasta or rice, millet, and corn bread. Environmental Factors: Viruses have been strongly implicated in the development of malignant tumors of the squamous epithelia including the oral squamous epithelium. Viral infections of latent or chronic nature are usually responsible for inducing malignant transformation by interfering with the host’s cell cycle machinery. These viral genes and gene products may affect cell growth and proliferation. Certain viral genes are proto?oncogenes which become oncogenes when inserted into the host’s DNA and ultimately resulting in malignant transformation. EBV causes oral hairy leukoplakia and ‘lymphoproliferative disease’ in immune-suppressed patients. HPV are the most common viruses implicated in oral carcinogenesis. Fungal Infections: Fungal infections caused by Candida species, in particular, Candida albicans has been implicated in the pathogenesis of oral premalignant lesions. Superficial fungal hyphae of Candida albicans have been found superimposed on leukoplakia, especially nodular leukoplakia, many of which have undergone malignant transformation. Candida infection can coexist or be associated with other risk factors like irondeficiency and in chronic smokers which may prove synergistic in the development of oral cancer. Immuno-suppression: Immuno-suppressed individuals are more prone to develop oral cancers. Human immunodeficiency virus (HIV)?infected patients are predisposed to developing Kaposi’s sarcoma and lymphomas, although not to OSCC. Immuno-suppressed organ transplant patients have been shown to develop lip cancers and the possible reason was attributed to increased exposure to solar radiation and other risk factors such as smoking. Occupational Risks: Occupational risks, namely exposure to excessive solar radiation/ultraviolet (UV) light is known to cause lip cancers. UV rays also causes actinic cheilitis which may transform to OSCCs. Sulfur dioxide, asbestos, pesticide exposures, and mists from strong inorganic acids and burning of fossil fuels have also been known to cause cancers of posterior mouth, pharynx, and larynx.[31] Certain occupations have been reported to place people at increased risk for the development of salivary gland carcinomas; these include manufacturing of rubber products, plumbing (exposure of metals), and woodworking in an automobile industry. Dental Factors: Poor oral hygiene, poor dental status (sharp/fractured teeth due to caries/trauma), and chronic ulceration from an ill-fitting denture has been suggested to promote neoplasm in the presence of other risk factors. There has been difficulty in obtaining the evidence whether dental factors influence oral cancer development. This is due to the presence of coexisting risk factors like smoking and alcohol consumption. In this study, mechanical irritation by scratching with a pulp cleaner has been shown to significantly increase the incidence of a chemical carcinogen induced tongue carcinoma. Syphilis: Tertiary syphilis had been known to predispose to the development of oral cancer along with other risk factors such as tobacco and alcohol. Radiation: Substantial evidence exists for a relationship between exposure to ionizing radiation and the later development of salivary gland tumors. The tumorigenic effects of therapeutic radiation to the head and neck on the salivary gland tissue have been assessed at the Michel Reese Hospital in Chicago. The mean annual incidence per 100,000 people was 48 cases in an early period, but increased to 77 per 100,000 people later in the study. It is clear from the above review that several risk factors are implicated in the development of oral cancer, of which the most common and established are tobacco smoking and betel quid chewing. Nevertheless, many patients are diagnosed with oral cancer despite abstaining from known lifestyle or environmental risk factors where factors like genetic susceptibility are believed to play the causative role. Hence, it is important for the public to be completely aware of the risk factors for oral cancer and it is prudent for dentists to look carefully for early signs of oral cancer, while routine examination of the oral cavity especially in patients with history of known risk factors.
