Cancer is on the rise in India: could air pollution be a factor?
Over the past decade or so, air pollution has been increasingly spoken about in India, particularly in the context of the deterioration of air quality across large parts of the country, especially in the winter months. The air we breathe is known to be linked to respiratory illnesses and even cardiac disease, but now, experts say, there is also a strong association with a disease that is a rising burden in India: cancer.
The scale of the cancer burden in India
Cancer numbers are rising, and rising fast in India. The Indian Council of Medical Research-National Cancer Registry Programme has projected that the number of cancer cases in the country will spike from 14.6 lakh in 2022 to 15.7 lakh in 2025. Approximately one in nine people in India is expected to face a cancer diagnosis during their lifetime, the ICMR estimates.
Cancer ranks second when it comes to non-communicable diseases that cause deaths in India. Lung cancer is the second-most common cancer among men in India, and also figures amongst the top five when it comes to women. Globally, it is the leading cause of cancer-related deaths, accounting for the highest mortality rates among both men and women.
Over the past two decades, doctors say there has been a concerning pattern emerging in India: a rise in the number of non-smoking lung cancer cases.
Traditionally, lung cancer has always been associated with smoking (which continues to remain the major risk factor) and its incidence has always been lower in India, compared to the West, says Kumar Prabhash, head, solid unit medical oncology, at Tata Memorial Hospital, Mumbai. 'Smoking rates have always been higher in the West and lower in India, and this was reflected in the lung cancer numbers. A large number of cases were associated with smoking, both in the West and India, in the past. Now however, and this is what we have been seeing over the past several years, there is a marked difference: a significant proportion of the lung cancer cases in India are in never smokers,' he says.
Estimates vary, but several doctors agree that up to 30% of lung cancer cases that are now being seen are in those who have never smoked.
At the Cancer Institute, Adyar, Chennai, two separate studies, one from 2012 and one from 2017, reflected this trend. In the first study, says Arvind Krishnamurthy, head of surgical oncology at the institute, researchers analysed patient data from 258 cases between 2003 and 2007, and found nearly 40% of the patients were non-smokers. In the second study, analysing data from 495 patients who came in during 2014-15, the non-smoking cases were over 55%,' he says.
There are other factors that are also playing out in this pattern, the histology (the way cancer cells and tissues appear under a microscope) of the cancers for instance, is different: while most smokers present with squamous cell carcinoma, in non-smokers the usual presentation is adenocarcinoma, mirroring a global trend in the rise of adenocarcinoma, says Dr. Krishnamurthy.
Age-wise, as with all cancers, patients in India are about a decade younger than those in the West, says Dr. Prabhash. Another concerning factor is that among women, the non-smoking lung cancers are higher than in men.
The shift, doctors say, points to the urgent need to look beyond smoking and tobacco exposure for causes of lung cancer.
Could air pollution be behind the rise?
There is no doubt, says Krithiga Shridhar, head, Cancer Epidemiology Unit, Centre for Chronic Disease Control, New Delhi, that both outdoor (ambient) air pollution in general, and particulate matter (PM) in particular, are Group 1 carcinogens, meaning that there is sufficient evidence based on human studies that they have the potential to cause cancer. Indoor (household) air pollution, meanwhile, is classified as a group 2 carcinogen, meaning the evidence is probable.
According to Swiss tech company IQAir's 2024 World Air Quality Report, India ranked as the fifth-most polluted country in the world with an annual average PM 2.5 concentration of 50.6 micrograms per cubic metre, against the World Health Organization's recommendation of 5, and higher than India's National Ambient Air Quality Standards of 40.
'The causal links are very well established between air pollution and lung cancer. The majority of evidence, however, is from settings where air pollution is low. From India, the evidence is still emerging,' Dr. Krithiga says.
Doctors point out that while at present they can state that there is a strong association between air pollution and lung cancer, more definitive evidence is needed from the country to establish it as a cause.
A 2022 research paper in the Indian Journal of Medical Research that described the epidemiology, and clinical profile of lung cancers in India, based on data from the National Cancer Registry Programme also notes this trend, and the potential role of indoor and outdoor air pollution. 'Compared to GATS (Global Adult Tobacco Survey) -1 (2009-2010), the prevalence of tobacco use has decreased in GATS-2 (2016-2017). Hence, there is an increasing recognition of the role of air pollution in the causation of lung cancer. According to recent findings of the National Non-Communicable Disease Monitoring Survey, almost half (48.5%) of the adults reported exposure to second-hand smoke at home, workplace or travel,' the paper states.
Another contributor may be indoor (household) air pollution, particularly among women, say experts. The burning of solid fuels and biomass for cooking could be behind this. 'Even though the use of solid fuels for cooking has declined with most households switching to gas, their use in the past may be a factor, as lung cancer has a long latency period and generally presents a couple of decades after the exposure to the cause,' says Dr. Prabhash.
Even in the northeast, says Ravi Kannan, director, Cachar Cancer Hospital and Research Centre, Assam, where the burden of cancer overall is the highest in India and where tobacco and alcohol use are major risk factors, the etiology (cause) of lung cancers is beginning to change, reflecting the larger Indian trend. 'Tobacco continues to remain a major cause of lung cancers here, but this is slowly shifting. The Northeast has always been one of the cleanest regions of India, but air pollution is beginning to be felt here as well. Also, in tribal communities, the fire is always kept burning, which could be a contributing factor, and while these traditional ways of life are changing now, it will take time for the impact of the change to be felt,' he says.
Air pollution may not be the only factor however: a research paper published last year in The Lancet Regional Health - Southeast Asia, 'Uniqueness of lung cancer in Southeast Asia', states that occupational exposure to asbestos, chromium, cadmium, arsenic, coal-based products, as well as genetic susceptibility and pre-existing lung disease, could all be contributing, and these are all factors that need to be researched says Dr. Prabhash.
The challenges of diagnosis and treatment
Lung cancer has one of the highest mortality rates when it comes to cancers in India. Its diagnosis, however, is often late. Primarily, says Partha Pratim Medhi, assistant professor, radiation oncology, AIIMS Guwahati, this is because its symptoms are nonspecific – cough, chest pain and shortness of breath are seen with other conditions as well. 'Even in X-Rays, very few healthcare professionals will first suspect lung cancer,' he says. Dr. Prabhash adds that in India particularly, doctors are more prone to suspect tuberculosis first, potentially delaying the diagnosis.
The 2022 research paper states that 'close to half of the patients had a distant spread of disease at the time of presentation in our analysis. Similar findings have been reported by studies from other Indian settings where most of the patients had Stage IV disease at the time of diagnosis.'
Of 10 patients he sees in a month, says Dr. Medhi, there is perhaps one who has lung cancer that is in stage 1 or 2. Four are perhaps in stage 3, and the remaining five in stage 4. 'By this time the cancer has metastatised, spreading to the bones, brain, liver and other parts, which is why survival rates are low,' he says.
While diagnostic facilities have improved over the years, with molecular testing now available to identify genetic changes and biomarkers to help with treatment plans, the infrastructure, for the most part, is still in tier 1 and tier 2 cities, making access an issue, says Dr. Prabhash.
When it comes to treatment options too, most are available in India, but affordability remains a challenge. Immunotherapy, which has been showing promising results in lung cancer in other countries, is only partially available. 'Some of these drugs are approved in India, while others are not. But even the drugs that are approved are extremely expensive, putting them out of the reach of most people,' says Dr. Medhi.
The way forward
At present, the way air pollution is viewed is very narrow, says Abhishek Shankar, assistant professor, radiation oncology, AIIMS, Delhi. 'It is now emerging as a serious killer and should be viewed as such,' he points out. Currently, he says, India reports about 75,000 new cases of lung cancer each year, but this is projected to go up to 1 lakh cases, calling for urgent action.
Data, say doctors, is what is needed: more research from India about the causes of lung cancer beyond smoking. 'While tobacco and smoking continue to be major risk factors, the pattern that has emerged now is well established, and we need to utilise this to find the links to the causes. Remember, air pollution is not only a risk factor for lung cancer – there is evidence for it across cancer sites including oral and urological, as well as childhood leukaemia,' says Dr Krithiga.
In addition to extensive, India-based research into the links between air pollution and cancer, the country also needs measures to combat pollution, experts say.
There is a window of opportunity in the Northeast now, to prevent the hazards of environmental pollution, says Dr. Kannan. 'We can intervene now, with a concentrated effort from the government, non-governmental organisations and civil society. The Northeast can learn, and equip itself to be able to prevent, and better handle cases in the future,' he says.
When it comes to the rest of the country, household air pollution has been progressively declining in India. 'It has not been fully tackled, but we are making progress, especially with the provision of cleaner sources of fuel such as gas,' says Dr. Krithiga. Outdoor air pollution presents more of a challenge, she adds. 'The sources of outdoor pollution are multiple, and our handling of it needs to be multi-sectoral. We are at the stage of acknowledging and finding ways to address the problem. This is the way forward.'
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