Expert opinion on the Linkage of Tobacco Use with Head and Neck Cancer
Head and neck cancers comprise of cancers affecting the upper aerodigestive tract. Oral cavity, nasopharynx, oropharynx, hypopharynx, larynx, thyroid gland and salivary glands comprise of subsites of head and neck region. The major bulk of head and neck cancers in India arise from the oral cavity, oropharynx, hypopharynx and larynx. Cancer of the oral cavity and oropharynx is the seventh commonest cause of cancer mortality in the world. Numerous epidemiologic studies have shown the association between use of tobacco and head and neck cancer. Tobacco usage in the form of smoking can cause cancers of the larynx, oral cavity, hypopharynx and oropharynx, while chewable tobacco is most often associated with oral cancers.
Tobacco burden and epidemiology
Tobacco-related cancers are responsible for 30-40% of cancer death and are considered a leading preventable cause of death.
It is estimated that one-third of the world’s adult population, and around 1.1 billion individuals, smokes tobacco, which makes every sixth human being a smoker.
India contributes to 28% of tobacco consumption in the world. The risk of developing head and neck cancers for cigarette smoking is 5-25 fold more than a non-user. The cancer risk steeply increases in a dose-response manner with increasing risk with an increase in the number of cigarettes smoked and increase are years of smoking. Even after cessation of smoking the risk of developing HNSCC decreases gradually over a period of more than ten years. Even second hand or passive smoking is also associated with an increase in laryngeal and pharyngeal cancer risk especially if the exposure is more than 15 years. Alcohol consumption is independently associated with increase in cancer risk for oropharynx and hypopharynx. Tobacco and alcohol consumption together have a synergist effect, which further accentuates the risk.
Tobacco smoking has become widely popular and socially acceptable in the 20th century accounting for a large number of tobacco-related deaths due to lung and heart disease, cancers. Even though the incidence of smoking has reduced due to increased awareness and government regulations. The risk of tobacco-related cancer was skewed towards the male, but in the recent decade, the risk ratio has tilted towards females making the risk difference between the genders narrow due to increase in the number of female smokers.
The risk of developing head and neck cancer by tobacco smoking ranges from 4.8-26.1% depending on duration and type of smoking while smokeless tobacco carries a risk of 17.6% of developing a head and cancer which is also dose and duration dependent.
Mechanism of cancer causation and effects of tobacco usage
Tobacco consists of more than 7000 harmful compounds. Carcinogens are compounds that have the ability to cause cancer. There are more than 60 potent carcinogens in cigarette smoking and at least 16 in smokeless tobacco. In both forms tobacco-specific nitrosamines (such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N′-nitrosonornicotine (NNN)), polycyclic aromatic hydrocarbons (such as benzo[a]pyrene) and aromatic amines (such as 4-aminobiphenyl) seem to have an important role as causes of cancer.
On the usage of tobacco carcinogens most often gets detoxified and removed from the body. But continued exposure there is metabolic activation causes DNA adducts (break in the DNA structure). A normal cell has the capacity to correct the DNA adducts and repair the damage caused by tobacco carcinogens. When there is persistent miscoding, mutations occur in the DNA makeup of the cell. Once tumour suppressor/oncogenes get mutated and the cell turns cancerous.
Persistent smoking can result in poor response to cancer treatment, more surgical complications; causes a decrease in survival and can also cause second cancers.
Prevention:
Most often people start using tobacco products generally at a young age because of effective marketing and peer pressure. Nicotine is the main component of tobacco. Nicotine is not carcinogenic but is extremely addictive, making quitting the habit a difficult task.
A most effective way to quit smoking is behavioural counselling combined with medications like nicotine replacement, bupropion sustained release, varenicline. Nicotine replacement is of the most efficient medication for motivated patients and also has the least number of complications when compared to varenicline or bupropion.
Awareness regarding the effects of tobacco and its related cancer, which has been accentuated by National tobacco control programme in the recent decade, we have seen a drastic fall in the number of tobacco users. Ban on tobacco products selling and usage in most areas under the NTCP has largely been responsible for fall in the number of smokers.
Screening for head and neck cancers can be done for high-risk subjects (tobacco users) to diagnose cancer early or in a precancerous condition. Various subsites of the head and neck are screened differently. The oral cavity can be screened with just clinical examination in visible light while screening of larynx or hypo/oropharyngeal regions will require endoscopy. Oral cavity screening by cancer specialist is essential in order to identify the signs of cancer early. Oral cancer screening is considered the most cost-effective screening with just six dollars spent per screening.
The way forward in reducing the incidence and mortality of tobacco-related cancers by strict tobacco control policy and tobacco cessation programs.
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