Smoke till you drop Light cigarette, inhale, exhale: tobacco smoke contains a total of 70 carcinogenic substances. Nicotine itself is not carcinogenic, it is merely addictive. And that is precisely what makes it so fatal.
Vienna – Statistically speaking, neither genes nor lifestyle are the main cause of some cancers. American oncologist Bert Vogelstein and bioinformatics specialist Cristian Tomasetti believe random mutation is to blame. To prove their theory, the pair have put forward a mathematical model to calculate the probability of developing cancer. Their starting point: malignant tumours occur when cell division goes awry. So the more mutations, the higher the risk.
Their hypothesis stated that organs with the most stem cells and higher division rates are also the most vulnerable to cancer. And for 22 of the 31 types of cancer studied, there was a correlation. The researchers calculated that while the lifetime number of stem cell divisions in the lower stretch of the intestinal tract amounted to around one trillion, the total for the duodenum was only around 10 billion. And colon cancer is significantly more widespread than duodenal cancer.
But Vogelstein and Tomasetti’s model does not compute for all cancers – lung cancer is a case in point. Rare until the start of the 20th century, bronchial carcinoma is now the second most common cancer in men, coinciding with increased tobacco consumption.
Toxic cocktail
Cancer risk can be directly measured against an exposure-response relationship. This means that the earlier a person picks up the habit and the more heavily or longer they smoke, the more likely it is that they will develop lung cancer. “A pack a day triggers an average of one mutation in the genetic information – that’s more than 7,000 over 20 years,” said Richard Greil, head of oncology at University Hospital Salzburg.
Of the 7,000 chemical substances in tobacco smoke, 70 are proven carcinogens including aerosol, cyanide, benzene, formaldehyde, methanol and acetylene. “Tars and hydrocarbons that have not been completely incinerated have carcinogenic potential,” noted Greil.
Chronic inflammation is an additional complication. “The mucous membranes in heavy smokers’ lungs are coated with tar,” added Wolfgang Hilbe, head of oncology at Vienna’s Wilhelminenspital. The fact remains that 85 percent of lung cancer diagnoses are directly linked to the consumption of tobacco and the remainder to environmental or genetic factors.
“The purely hereditary form of lung carcinoma is relatively insignificant. While there are increased rates within families, in the majority of cases this can be explained by the fact that children of smokers are significantly more likely to smoke and have already been exposed to passive smoking while young,” Wolfgang Hilbe clarified. Inhaled carcinogens from asbestos, arsenic, cadmium, chromium, nickel and polycyclical aromatic carbohydrogens such as those found in asphalt tar all cause lung cancer.
While rates are still higher among males, women are closing the gap. In Austria, around twice as many women are affected as 20 years ago – a direct result of increased tobacco consumption, experts believe. In the USA, more women are now dying from lung carcinoma than from breast cancer.
Puff by puff
But it is not just active smokers who are in danger. Several studies have shown that passive smoking increases the risk of contracting lung cancer by between 30 and 40 percent. “An evening in a smokefilled bar – the lungs can handle that easily. But if a waitress who is a non-smoker works in a smoky bar then we are talking about an imminent health risk,” Hilbe emphasised.
There is still widespread belief that young people’s cells still have effective immune and repair me- chanisms that can counter the toxins in tobacco smoke. But the opposite could be true: studies suggest that developing bodies in fact react more sensitively.
Studies show that former smokers who regularly consumed tobacco before the age of 15 suffer more damage to the genetic material in the tissue of the lungs on average than former smokers who did not become addicted to nicotine until after the age of 20. It should be noted that though nicotine is not carcinogenic, it is highly addictive. For Greil as an oncologist, offering better protection for future generations is paramount. “As far as young smokers are concerned, the situation in Austria is catastrophic. We are the worst in Europe,” Greil said.
And prevention has to begin much earlier than the “critical puberty stage. We need suitable role models and long-term concepts that start at kindergarten age and continue until at least the age of 16.” What is clear is that conventional educational and informa- tion programmes do not work. “It is about as effective as trying to tell a teenager that they should start putting money aside for their pension,” Hilbe added.
In the majority of cases, a diagnosis of lung cancer comes at around the age of 60, but anyone who thinks that they can continue smoking until middle age is mistaken. “However, even people who do not stop until they are 50 can significantly lower their risk of dying from lung cancer,” Greil said. After five years without smoking, the risk of contracting the disease falls by 60 percent.
Race against time
Another problem is that lung cancer is usually discovered at a late stage. A study in England and Wales showed that only around a third of patients were still alive a year after being diagnosed. After 10 years, survival rates dropped to just five percent.
Canadian epidemiologist Prabhat Jha from the Center for Global Health Research in Toronto has clearly demonstrated the health risks of cigarette smoke. He analysed data from around 113,000 women and 88,000 men over a period of 25 years. The central finding: a lifelong non-smoker is twice as likely to live to 80 as a smoker. However, the difference in life expectancy cannot be attributed to lung cancer alone: smoking is also a major cause of COPD, coronary heart disease, stroke and 16 other types of cancer.