The tobacco & cancer connection

Chewing tobacco and gutkha primarily cause oral cancers while smoking causes laryngeal and lung cancer. Read on to know more about the carcinogens in tobacco and how they affect our body Smokeless tobacco and smoking are equally harmful. The primary sites affected by each are different. Dr Devendra Chaukar, surgeon, Tata Memorial Hospital says, “Chewing tobacco and gutkha primarily cause oral cancers while smoking causes laryngeal and lung cancer. Additional substances used in smokeless tobacco also cause mucosal damage.”
Not only are tobacco chewers and smokers at a risk of cancer, but second hand smoke causes lung cancer in non-smokers. Though low, there is a definite risk. Workplace exposure to tobacco smoke increases risk of lung cancer by 12%-19% in non-smokers. In the spouse of smokers, the risk is about 20% in females and 30% in males.

Cancers caused by tobacco
•    Head and neck cancer, which include oral, oropharyngeal, nasopharyngeal and laryngeal cancers
•    Lung cancer
•    Oesophagus cancer
•    Stomach cancer
•    Pancreatic cancer
•    Renal cell carcinoma
•    Cervix and vulva cancer
•    Urinary bladder cancer
•    Hepatocellular carcinoma
•    Leukemia and lymphoma

Carcinogens in tobacco
Dr Chaukar says, “DNA damage forming various chemical compounds leading to inactivation of tumour suppressor gene p53 and activation of proto oncogene KRAS. Nicotine is the addicting substance in tobacco smoke. However, it is not carcinogenic by itself. Various additive substances used in tobacco products enhance the absorption of nicotine by different mechanisms, like menthol numbs the throat and leads to increased consumption; others reduce alkalinity of the product and increase unprotonated nicotine that is easily absorbed.”

Some of the carcinogens present are:
•    Polycyclic aromatic hydrocarbons
•    Heterocyclic compounds
•    N- nitrosamines
•    Aromatic amines
•    Heterocyclic aromatic amines
•    Aldehydes
•    Phenolic compounds
•    Volatile hydrocarbons
•    Nitrohydrocarbons
•    Other organic compounds, metals like arsenic, beryllium, nickel, chromium, lead, cadmium and radioactive compounds like cobalt and polonium.

Effect of tobacco carcinogens on the body
Many tobacco carcinogens are inactive and require activation by means of various body enzymes. Also body has innate defence mechanism by means of detoxifying these harmful substances
Dr Chaukar explains, “The balance between carcinogen metabolic activation and detoxification varies among individuals and is very likely to affect cancer susceptibility with those having higher activation and lower detoxification capacity being at higher risk. In individuals genetically susceptible to early chromosomal damage to tobacco due to deficiencies in protective mechanisms show cancers at early age and after exposure to tobacco for short duration.”
Warning signs of cancer in smokers
•    Lung cancer can present as cough,hemoptysis (blood streaked sputum), breathlessness, easy fatigability or neck nodes.
•    Oral cancers can present as premalignant lesion like leukoplakia (white patch), erythroplakia (red patch), and progressive difficulty to open the mouth called oral sub mucous fibrosis or as frank malignant ulcer, usually painless and non-healing.
•    Laryngeal cancer present as change in voice-hoarseness.
•    All head and neck cancer can present as palpable neck nodes without awareness of primary lesion.
•    Many other cancers, particularly intra-abdominal are detected incidentally. Usually they present late.   
Survival rates
Chances of survival if cancer is detected early are good provided tobacco and other habits are quit. Dr Chaukar elaborates, “The survival is good owing to availability of wide variety of options of curative treatment like surgery, chemotherapy and radiotherapy with low morbidity.”
When cancer is present late, treatment may not be necessarily with curative intent, but with palliative intent. Dr Chukar says, “Few cancers have poor prognosis when they present late that active treatment is not feasible. Liver and pancreatic cancers are classic examples, which are usually diagnosed very late and even with any possible treatment there are no survivor at 5 years. Any form of treatment takes its toll and are associated with functional impairment of some extent or cosmetic disfigurement, severe life threatening side effects of chemotherapy and intolerance to radiotherapy.”