Health

India's Cancer Incidence Rate Among Lowest in the World – but for How Long?

A recent article in the Indian edition of a newspaper showed how often the methods behind cancer data collection and interpretation are misunderstood, giving rise to flawed arguments about what we need to do next.

India has some of the highest numbers of cancer cases in the world but has some of the lowest rates of cancer in the world. For anyone, there can be hardly be a more contradictory statement. However, this statement is as much true as it is completely non-contradictory.

For most, it is confusion, and one of the outcrops of that confusion recently appeared as an oped in the Business Insider (BI), which cited an Institute for Health Metrics and Evaluation (IHME) report, in turn based on a paper recently published in the journal JAMA Oncology.

The Global Burden of Disease (GBD) project is an initiative by the IHME, which provides impartial global-level (and now state- or province-wise for many countries, including India) health trends to inform policymakers, researchers and funders. The paper in JAMA Oncology, like the report discussing the findings, was authored by researchers from the IHME.

Among other things, this report stated that India was in the list of countries with the lowest incidence rate of cancer development (lowest rates of development of new cases of cancer per 100,000 or 1 lakh population), albeit at the bottom. India’s rate (106.6 per 1 lakh population) was much lower than that of countries like Australia (743.8), New Zealand (542.8) and the US (532.9), which were in the list of countries with the highest incidence rate of cancer.

Developed countries fare worse

As one of the cancer experts from India and a co-author of the journal article in JAMA Oncology, I have observed a number of opinions and comments on this work appear in Indian media. One such piece was the oped in BI, which argued on a flawed basis that the incidence of cancer in India could not be one of the lowest in the world. The principal thrust was that there were a lot of missed cases of cancer in India due to which the incidence rates reported for India were fallaciously low. To make this case, the BI piece had quotes from two oncologists and cited two reports, by Ernst and Young report and The Lancet. While what the oncologists and the two reports had stated were mostly true, they were used to build a wrong argument.

The BI piece’s first question was: “For a country with such a large population, how are India’s rates of cancer so low?” The first thing to know about incidence rates is that they are the number of new cases per unit of population (mostly per 100,000 people) per year. Therefore, rates are adjusted for population and can be compared across countries with different population numbers. So, because of its large population, the number of cancer cases in India is also high. But when we create a rate, the number becomes small because the denominator is large. And when it comes to rates: the incidence rate of cancer in India is much lower than in developed countries.

The BI report then went on to claim that “it was an issue of data reporting”. For this, it quoted two oncologists who talked about missed cancer cases and how India had the third highest rate (it doesn’t) of female cancer cases in the world, after China and the US. It is true that in developing countries around the world, including India, cancer cases don’t always manage to reach a doctor since they are in remote parts of the country or the people don’t have the resources to avail medical facilities.

However, using this information to argue that India’s cancer incidence rates might be much higher is not appropriate. It shows a lack of understanding of how cancer registries work and how the GBD method for cancer works. Further, while it is true that the number of breast cancer cases and deaths in India are among the highest in the world, along with China and the US (Figure 1), the death rates of breast cancer in India are much lower than in developed countries (Figure 2).

Number of deaths due to breast cancer in the world. Credit: GBD Compare

Number of deaths due to breast cancer in the world. Credit: GBD Compare

The numbers of deaths are highest in China, India and the US, which light up in the yellow-red part of the spectrum.

Death rate per 100,000 due to breast cancer in the world. Credit: GBD Compare

Death rate per 100,000 due to breast cancer in the world. Credit: GBD Compare

When it comes to death rates, we clearly see that the developed countries in Europe, Australia and North America light up in the red-yellow part of the spectrum because their rates of incidence are higher than India’s and China’s, which are in the blue part of the spectrum.

Role of cancer registries

Then, the BI piece refers to an Ernst and Young report, which discusses the dismal state of India’s cancer detection system, with very few mammograms and PET-CT scans. While this is true and an important reason for why our cancer case detection rates are so low, it is still not the reason for the lower incidence rates of cancer in India. The piece talks about a Lancet study which had found that 70% of those with cancer in India die early because of a lack of awareness, lack of early detection and lack of access to proper medical care. While the number of deaths due to this is high, the death rates are still low in India (as shown in the figures above), something which hasn’t been cleared by the piece’s author.

According to the Ernst and Young report, India’s incidence rate is around 94 per 100,000; the author speculates that it must be higher: around 150-200 cases per 100,000 due to deficiencies in data collection and screening.

Overall, the BI oped stands for how often the methods behind cancer data collection and interpretation are misunderstood.

While we know that the number of cases may be high, due to high population the rates can be lower. Our estimate for the incidence rates come from cancer registries that cover population in a specific area and precisely capture every cancer case that occurs in that particular group. These registries make sure that the number of missed cases is as low as possible (less than 1%) so that the incidence rates as a result are accurate.

For our study, the authors accessed data from around 40 population-based cancer registries from India and combined them with with the GBD cancer methods to create an accurate cancer incidence rate estimate for India. The GBD cancer methods are published openly and are peer-reviewed by experts. Our findings themselves were published only after a global consensus on the methods and the findings were reached. Thus, the cancer incidence rates for India, which arise from cancer registries and the GBD cancer methods, are highly accurate, without much bias and unaffected by missed or under-reporting of cancer cases.

Two kinds of transitions

But what could be behind the low incidence rates of cancer in India? There are two main population changes happening in countries around the world, and they generally go hand in hand. They are demographic transition and epidemiological transition. With economic development, countries reduce their birth and death rates and the population pyramid becomes rectangular – i.e. the number of old people increases while the number of children and young decreases. Also, with economic development, infectious diseases are slowly being replaced by chronic diseases. The effects of these two transitions is reflected on the cancer rates as well.

Further, the main risk factor for cancer is ageing: the longer one lives, the higher is their chance of developing cancer. In developed countries like Australia, New Zealand and the US, life expectancy is high and people live longer, due to which they have a higher risk of developing cancer. This shows up in the high incidence rates of cancer. In India, which is still a developing country, people don’t live long enough to increase their cancer risk substantially. Thus, at a population level, the incidence rates of chronic diseases such as cancer are much lower in India than in the developed world.

Cancer risks other than ageing have also been lower in India; there is also some evidence of certain Indian diets being able to protect against cancer. However, this will not be the case for much longer. India is developing quite fast economically, and with that the Indian population will inevitably undergo rapid demographic and epidemiological transitions together with an increased exposure to risk factors for cancer.

One of the findings of the JAMA Oncology article was the rapidly increasing number of new cancer cases in developing countries – with a 31.9% increase (16.6% due to population growth and 15.3% due to population ageing) in new cancer cases in low-middle SDI countries (which includes India) between 2006-2016. While it might be difficult to reduce the pace of rising cancer cases and rates, we need to do something to catch it early so that people live longer, and so cancer becomes a chronic disease rather than a death sentence.

Subhojit Dey is Executive Director at Disha Foundation.