Tobacco, lung cancer and non-smoking lung cancers

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Published: 29 Mar 2017
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Dr Preetha Rajaraman - NCI Centre for Global Health, New Delhi, India

Dr Rajaraman speaks with ecancer at EBMCI 2017 about lung cancer, from its global incidence to an increasing trend in India.

She notes air pollution as likely contributors in Indian populations beyond tobacco use, and highlights that quitting smoking at any time in life can improve health and cancer risk.

Dr Rajaraman does note second hand smoke as a risk factor, though other causative pollutants vary by region, with indoor air pollution a notable risk in India.

Lung cancer screening is also discussed by Dr Christine Berg here.

For several decades now lung cancer has actually been the most common cancer in the world with about 1.8 million new cancer cases that were estimated in 2012 and 1.6 million deaths from lung cancer. Now, as you can see from these numbers in fact the mortality very closely mirrors the incidence because unfortunately lung cancer still remains a very fatal disease.

Until recently this disease was a disease of high income countries, the US, Europe etc., but the other shift that has happened in the last few decades is that this is moving to the rest of the world. In fact, if you look at the rates themselves in India they’re still lower compared to a country like the US but if you look at national registry data here in terms of cancer trends you will see that the rates are increasing and that’s particularly true in women actually.

What are some of the reasons for this increase in cancer rates?

There are a couple of different things going on. Certainly the most important risk factor by far for lung cancer is tobacco smoking and those rates have certainly increased in India. That’s your most obvious risk factor but the second thing that’s going on is that the burden of non-smoking lung cancer is actually also quite high around the world. In fact, if you look at places like India and China this becomes particularly important because you have factors such as indoor and outdoor air pollution that also contribute to lung cancer. I certainly think these are probably contributing but there isn’t very much data on that from this part of the world.

Is smoking as a cause of lung cancer a large factor in India?

Certainly we’ve known that smoking is a cause of lung cancer right from the 1950s. This is, in fact, one of the ways that much of the methodology that we’ve developed for modern epidemiology was actually formed in trying to answer this question. So we know tonnes at this point about what kind of doses of cigarettes cause what kinds of cancers; which histologies of lung cancer are more susceptible to cigarettes and other kinds of products. We also know very simply that the more you smoke the higher your risk. We know that if you quit smoking that risk goes down. There was a very nice paper a couple of months ago that showed that it’s never too late to quit smoking so even if you quit when you’re in your sixties your risk still goes down compared to current smokers.

What a lot of people don’t realise, because smoking is such an overwhelming risk factor for lung cancer, is that if you look at the numbers of non-smoking lung cancers those are actually quite large as well. So, in fact, if you look at that as an entity separate from smoking lung cancer it would in fact be the seventh leading cause of cancer death globally. There are many theories as to why those rates are going up and in fact there is a question, indeed, of are those rates going up? But we do know that there are known carcinogens that are associated; one of those is radon, also second-hand smoke, indoor and outdoor pollution, several dietary factors and so on. But depending on where you are in the world the distribution of which of those factors is really more important changes quite a bit.

Where would you like to see the primary efforts for reducing lung cancer?

Certainly I think for many decades now there has been a very strong movement to stop tobacco products and that should absolutely continue because that is still the bulk of lung cancers. There are some very well-researched, proven strategies for how to do that and we need to continue that. On the other hand, I do think there hasn’t been enough attention, particularly in these parts of the world, on how much of a risk there really is from ambient as well as indoor air pollution and I do think we need to generate more research, for one, from this part of the world because even though the exposures are highest here most of the research has actually been done in countries where the air pollution and ambient air pollution is quite low in fact. So we do need more of that here but at the same time we know that air pollution, whether it’s indoor, whether it’s kitchen air pollution does cause cancer and there are ways to reduce this. So we need to be looking into what’s causing these emissions and trying to minimise those, certainly in terms of kitchen exposures, moving to clean cook stoves rather than biomass fuels.

What was the take-home message from your talk?

Tobacco is the single most important risk factor for lung cancer and we need to continue our efforts to stop the use of tobacco products. However, we can’t ignore the fact that there’s also a large burden of non-tobacco related lung cancer and we need to understand a little bit more about what are the risk factors for those, particularly in situations like India where there’s very little research on this. At the same time we do know from other parts of the world that both indoor and outdoor air pollution are proving human carcinogens and so we need to look into how to minimise those exposures here. Certainly I would also say that awareness is still not very high here and there needs to be much more focus on spreading awareness of the fact that these are also carcinogens.