Causes of cancer

Introduction

Cancer by its very nature is an abnormal, seemingly unrestricted growth of body cells that is well distinguished from other forms of illness. In much simpler words it could be understood as when a normal cell “breaks out” of its cell cycle, “rebels”, starts dividing recklessly, invades distant tissues, uses body resources, has the capability to create its own resources for its unrestricted growth and eventually begins killing the body it lives in. This complex disease is a major cause of morbidity and disability, second only to heart disease as cause of death among Americans. Although this breakout may occur at any age, cancer is predominantly a disease of aging as time is needed for the cellular events involved in the development of cancer to take place. The use of tobacco and alcohol significantly increase the risk involved in cancer. The role of other factors in promoting cancer remains important, but unclear.

Factors increasing the risks of developing cancer

  • If you use Tobacco in any form
  • If you practice any other tobacco related habit
  • If you are an Alcohol user
  • If Your Diet is lacking adequate nutritional elements
  • If you are overweight or obese
  • If your immune system is weak, leaving you unprotected against cancer
  • If you have suffered from Chronic infections like gastric ulcers, hepatitis B (HBV), hepatitis C (HCV), or genital warts (HPV)
  • If your work put you in a high risk environment of developing cancer
  • If you suffer from chronic irritation caused by dentures/ sharp tooth or improper restorations

Tobacco use and cancer

Tobacco was first introduced to western civilization by the Spanish explorers of America in the early 16th century. At first, it was simply smoked in pipes, but as it became more popular it was also chewed and snuffed. Cigarettes were first made in Spain in the mid- 17th century and in the 20th century they became the popular form of tobacco habit. The first known suspicion of the association of tobacco and the formation of oral cancer dates back to the 18th century, when cancer of lip was predominantly noted among tobacco users. One study demonstrates that 80% of patients of oral cancer were found to be smokers.

Let’s understand what we inhale while smoking

In the combustion mainstream of one cigarette there are approximately 500mg of gas (92%) and particulate matter (8%). 85% of the gaseous phase is composed of oxygen, carbon dioxide and nitrogen. Even though the percentage of carbon monoxide is low, it raises blood levels of this gas significantly, in turn influencing the haemoglobin- exchange system. “Tars” (aromatic hydrocarbons) range from less than 1 to 35 mg and contain the most potent carcinogens (cancer causing agents). Nicotine ranges from less than 1 to 3 mg and contributes to habituation, platelet adhesion associated with cardiovascular disease, ulcer susceptibility from decreased pancreatic bicarbonate and hypertension. Cancer causing agents (Carcinogenic agents) have been successfully isolated from tobacco products including nitrosamines, polycyclic aromatic hydrocarbon, nitrosodiethanolamine, nitrosoproline and polonium.

Pipes, cigars, snuff and other smokeless tobacco

  • Pipe smoking has proven to be directly related to the cancer of lower lip
  • Snuff placement causes an epithelial dysplasia and gradually carcinoma at the site of its placement particularly the gingiva and buccal mucosa
  • Nitrosamines (N- nitrosonornicotine being the most potent) have being identified as non-combustible products in chewing tobacco and snuff with carcinogenic property
  • Interestingly tobacco products are not regulated by the Food and Drug Administration and the nitrosamines content far exceeds those permitted in food as preservative

How tobacco can kill even after quitting the habit

The hazards of smoking do not end at cancer formation but continue further as it decreases the survival time for the patients post diagnosis and treatment. The mortality rate from oral carcinoma is much higher in smokers when compared to non smokers. The effects of smoking diminish only 5-10 yrs after the cessation of this habit.

Other carcinogenic habit forms

Social customs associated with cancer are complex and wide ranging.

  • In areas of world where habits like betel and tobacco dipping are practiced, the incidence of oropharyngeal tumors is high.
  • In India, oral carcinoma accounts for a high percentage of total cancers ranging from 15 to 65% with maximum concentrations in South.
  • A strong evidence for this distribution is the more prevalent use of various forms and combinations of tobacco, slaked lime, betel nuts and spices.

Another habit commonly observed is “reversed smoking” (placement of the lit end of the cigar/tobacco leaves inside the mouth) and is frequently related to palatal cancer.

Alcohol, cirrhosis and cancer

Death from cirrhosis (primarily due to Alcohol intake) is the eighth leading cause of death in the US. This high incidence is relevant for us because alcohol intake has been related to a high risk of developing oral cancer and a higher-than-expected mortality. This may be related to:

  • Alcohol dehydrates the mucosa and leaves it more susceptible to the action from carcinogens present in alcoholic beverages (nitrosamines, hydrocarbons) or,
  • Induced cellular changes in the live.
  • Due to the combined effect of the consumption of alcohol and smoking, as most chronic alcohol consumers are chronic smokers too.

Is your diet too little or far too much

  • Dietary factors such as high fat and low fiber may play a role in carcinogenesis.
  • Deficiency of antioxidants, vitamins and nutrients has been postulated as cofactors in carcinogenesis. Low dietary and/or serum levels of Vitamin A have been associated with oral premalignant lesions and the subsequent formation of malignancy.
  • This association has been based on the correlation between Vitamin A deficiency and hyperkeratosis.
  • As for Vitamin C it appears to help block the conversion of nitrites to nitrosamines (potent carcinogens).
  • Zinc and copper have also been implicated in head and neck cancer.
  • Paterson- Brown- Kelly syndrome shows an association between iron deficiency and postcricoid carcinoma.
  • People above 10 yrs of age who consume Salted Fish diet are at a high risk for nasopharyngeal cancer due to nitrosamines.

Nutrition is also an important factor in the management of patients during the phase of treatment and rehabilitation. Poor nutrition or abnormal weight loss are usually a sign of poor prognosis indicating cachexia and intercurrent infections. Obesity also is associated with a poor survival.

Your immune system as your defence against cancer

  • Our immune system is our best chance against every war our body fights against all the intruders from the environment. Hence, having a normally functioning immune system ensures proper surveillance of the cell activities occurring at all times. With growing age, our immune competence gradually diminishes, which can undoubtedly be linked to the association between age and malignancy.
  • Furthermore studies have shown that the risk of cancer increases in individuals whose immune systems are either congenitally defective or have been suppressed due to disease or chemotherapy. Strong chemotherapy against an infection can cause your immune system to take a back seat while the medicines are fighting the war against that infection, this in turn renders you open to attack by other infections and eventually even cell surveillance suffers leaving a window open for cancer to occur.
  • An immunodeficient state with a strong correlation to cancer is AIDS (Acquired Immune Deficiency Syndrome).

History of chronic infections

  • Among all the infectious agents the role of viruses as a causative agent for the formation of cancer has been a matter of mass speculation over a long time
  • Those that are known to have a carcinogenic effect are divided into two broad groups: herpesvirus and papillomavirus.
  • Herpes Simplex Virus-1 and Herpes Simplex Virus-6 proteins are frequently expressed in oral cancer cells, whether this indicates an active role of the virus in the carcinogenesis is still unknown.
  • HPV infections are common sexually transmitted infections and are of two types- low risk HPVs which do not cause cancer but are responsible for skin lesions or warts and the second type is high risk HPVs.
  • The high risk HPVs are also called oncogenic HPVs and have the potential to cause cancer.
  • The principle high risk types are Type-16 and type-18 found in most Cases of cervical cancer and is believed to be the causative agents of that malignancy as well as anal cancer in persons with HIV or practicing unsafe sex.
  • HPV-16 may play a role in the neoplastic transformation of the precancerous lesions into malignancy.
  • Other Infectious agents associated with increased cancer risk include hepatitis B virus (liver), the bacterium Helicobacter pylori (stomach) and human immunodeficiency virus (many sites).

Environmental and occupational risk factors

Several environmental factors affect the probability of the occurrence of cancer.

  • Some of these agents include X-rays, UV light, viruses, tobacco products and pollutants and many other chemicals.
  • Passive smoking can cause cancer of lungs, esophagus, bladder and pancreas.
  • Radiation exposure is high in professionals working on a daily basis in close proximity to such radioactive sources like radiologists, radio-technicians and nuclear power plant workers, these people need to constantly keep a check on the amounts of radiations they are exposed to and hence PERSONAL MONITORING DEVICES are used extensively.
  • UV light is associated with most skin cancers, including the deadliest form called melanoma.
  • Many industrial chemicals are carcinogenic including benzene, other organic solvents and arsenic.
  • Factory workers who are in constant exposure to nickel and chromium dust are at a high risk of nose/larynx/paranasal sinus carcinomas.
  • Hardwood dust is particularly carcinogenic for adenocarcinoma of paranasal sinus.

Some cancers associated with environmental factors are preventable. Simply understanding their dangers and avoiding them can minimize the risks of development of cancer.

Knowing your work place and the agents present they can place you at an upper hand, as with cancer, “Prevention is better than the cure” Various agents like metals, chemicals, radiations are used in industries which can also affect the probability of occurrence of cancer among the workers of associated fields.

Metals

  • Arsenic: It is produced commercially as a by-product of nonferrous metal production, primarily from copper production, comprising greater than 10% of dust content in some smelter operations. Inorganic arsenic is primarily used to preserve wood, but is also used as a pesticide mainly on cotton plants.
  • Beryllium: It is used in the nuclear, aircraft and medical devices industry. Used also as an alloy or in specialty ceramics for electrical and electronic applications. Found as a contaminant in the combustion of coal and fuel oil.
  • Chromium: It is used in steel and other alloy production. Chromium III and Chromium VI are used in chrome plating, the manufacture of dyes and pigments, leather tanning and wood preserving.
  • Nickel: It is used primarily as an alloy in stainless steel. Also used in nickel plating and battery production.
  • Lead: It is used primarily in the production of batteries, ammunition, metal products such as solder and pipes and devices to shield X-rays. Lead is also found in gasoline, paints, ceramic products, caulking, and pipe solder.

Pesticides

It is used for preventing, destroying, repelling or mitigating any pest or in use as a plant regulator, defoliant or desiccant. They are also used in agricultural applications, although residential application is also an important source.

Petrochemicals and Combustion Products

Petrochemicals are derived from natural gas or petroleum and used to produce a variety of other chemicals and materials including pesticides, plastics, medicines and dyes. Mainly result from the incomplete combustion of burning coal, oil, gas (diesel exhaust), household waste, tobacco and other organic substances. Dioxins are a class of chemical that are the by-products of combustion processes containing chlorine and carbon-based chemicals such as polyvinyl chloride (PVC) plastics. Dioxins are also created during the chlorine-bleaching processes for whitening paper and wood pulp.

Radiation

  • Ionizing: Any one of several types of particles and rays given off by radioactive material, high-voltage equipment, nuclear reactions, X-rays and gamma rays are radiation particles of concern to human health.
  • Non–Ionizing: It is comprised of microwaves and electromagnetic frequencies including radio waves and extremely low-frequency electric and magnetic fields. Cellular and mobile cordless telephones emit radio frequencies in the microwave region of the electromagnetic spectrum. Radio frequencies at 300 MHz are created by radio, television, wireless telephony, emergency communications and radar among other sources.

Solvents

  • Benzene: It is used as an intermediate in the production of plastics, resins and some synthetic and nylon fibers. It also used to make some types of rubbers, lubricants, dyes, detergents, drugs and pesticide and is also found in crude oil, gasoline and cigarette smoke.
  • Carbon Tetrachloride: It is used primarily in various industrial applications. Before being banned, was also used in the production of refrigeration fluid and propellants for aerosol cans, as a pesticide, as a cleaning fluid and degreasing agent, in fire extinguishers, and in spot removers.
  • Methylene Chloride: It is used primarily as a solvent in a variety of industrial applications and as a paint strippers. It may also be found in some aerosol and pesticide products and in the production of photographic film.

These are just some of the commonly found carcinogenic agents present in things we use on a daily basis. Others like xylene, a solvent used in rubber and leather industries, toluene, present in paints and varnishes etc require a check when used on a regular basis.

Dentures, fillings and sharp tooth edges

  • Although some cancers have been known to develop in areas adjacent to prosthesis or covered by an appliance, it is not conclusive whether this is coincidental or a cause-and-effect relationship. In some cases though chronic irritation working in addition to other unidentified factors may possibly promote neoplastic activity.
  • Any area whether under direct irritation due to prosthesis, or due to any indirect irritant can undergo epithelial changes pertaining to the development of carcinoma in situ.
  • Care should be taken on the part of dentists as well as patients to minimize local irritation and to examine any changes with utmost care.

The same principle of chronic irritation may be applied to patients with poor oral hygiene or jagged teeth or fillings that may act as irritants on the adjoining mucosal areas. Dental material has not been shown to be carcinogenic

References


  1. SILVERMAN’S ORAL CANCER- 4th Edition, Chapter: Etiology and predisposing factors.
  2. AMERICAN CANCER SOCIETY: Guidelines on Diet, nutrition and cancer prevention: Reducing the risk of cancer with healthy food choices and physical activity.
  3. BURKET’s ORAL MEDICINE,DIAGNOSIS AND TREATMENT- 11th Edition, Chapter- Oral Cancer: Etiology
  4. COLOR ATLAS OF CLINICAL ORAL PATHOLOGY- Brad W. Neville- 2nd edition
  5. REDISCOVERING BIOLOGY:Molecular to Global Perspectives: Cell Biology and Cancer
  6. ENVIRONMENTAL AND OCCUPATIONAL CAUSES OF CANCER- Richard Clapp, Genevieve Howe, Molly Jacob Lefevre, Prepared by Boston University School of Public Health and Environmental Health Initiative, University of Massachusetts, Lowell.
  7. FACT SHEET ON CANCER-WORLD HEALTH ORGANISATION
  8. CANCER- Malcolm R.Alison, Imperial College School of Medicine, LONDON,UK
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Dr. Sanjay Soni

MDS (Oral and Maxillofacial Surgery) | Reader (MN DAV Dental College and Hospital)

MN DAV Dental College, Solan

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