The Role of Cancer Research in Noncommunicable Disease
The Role of Cancer Research in Noncommunicable Disease
A number of research areas would provide vital evidence in establishing the most reliable evidence base for cancer control. Some that are particularly relevant to low- and middle-income countries are described below.
Improved Surveillance of Cancer Morbidity and Mortality and Prevalence of Major Risk Factors. Coverage of cause-of-death statistics is essential and is still lacking or incomplete in more than half the world's countries. To plan cancer services, governments need to know not only how many people are dying but how many will develop the disease and how many will live with it as cancer survivors. An understanding of temporal trends in the population prevalence of major cancer risk factors complements cancer surveillance to improve long-term cancer projections and planning. Cancer registries provide a platform for research, in addition to cancer statistics. They reveal geographical heterogeneity and temporal trends that generate etiological hypotheses. Registries are also vital in assessing the outcome of prevention-associated interventions, including community-randomized trials and planned public health interventions (eg, cervical cancer screening, early detection of breast cancer and HPV, or HBV vaccination). Population-based cancer registries are integral to both cancer control and research and as such should be a core component of any noncommunicable disease surveillance plan. Sadly, such registries are lacking or inadequate in many countries, especially in developing regions of the world. Sufficient knowledge and experience exist to provide support to countries to develop cancer registries that, with a modest level of sustained investment, would cover a defined region of a country, comprise a minimal dataset, and use open-source software (eg, CanReg5) to allow standard analyses and international comparisons. The IARC-led Global Initiative for Cancer Registry Development in Low- and Middle-Income Countries is an international cooperation designed to create regional centers of expertise in cancer registration, which in turn will provide the infrastructure to transform the coverage and quality of registration.
Cancer Etiology. The four shared noncommunicable disease risk factors require further research in relation to cancer. Examples of the research required are the need for more precision about the type and amount of physical exercise required to reduce cancer risk as well as a better understanding of the risks associated with specific nutritional and metabolic factors. Nevertheless, cancer also differs from other noncommunicable diseases in that risk factors for a number of major cancer sites remain poorly defined. Examples of common cancers where information on etiology is lacking include prostate cancer, colorectal cancer, leukemia, lymphoma, kidney cancer, and a substantial proportion of breast cancer. For other cancers, such as esophageal cancer, carcinogenic agents are known in developed countries but are less well understood in developing countries. Consequently, it is vital that research into the causes of cancer proceeds in parallel with research into prevention and implementation. Priorities for low- and middle-income countries should be focused on cancers that are common in the region and for which the risks cannot be easily inferred from previous research in high-income countries, either because investigations are lacking or because risk factors differ. In addition, exposure over the life course, including early in life, merits further study.
New knowledge about carcinogenic mechanisms and technologies to investigate biological changes subsequent to specific exposures offers important new opportunities to investigate cancer etiology. Progress in molecular cancer epidemiology is fundamental to moving forward in areas that have been refractory to yielding conclusive public health advice in recent years.
Prevention Research. Low-income countries have different cancer incidence patterns compared with high-income countries, notably in relation to cervical, liver, stomach, and HIV-associated cancers ( Table 1 ). As mentioned above, for some cancers, the challenge is to implement established interventions; for other cancers, the research priority should be to identify prevention strategies. For example, H. pylori infection is a well-established risk factor for stomach cancer, the second leading cause of cancer death worldwide, and yet optimal H. pylori eradication and its impact on stomach cancer incidence remain to be defined. Although HBV is associated with a majority of liver cancer cases worldwide, there are 350 million chronic HBV carriers whom HBV vaccination cannot help and in many HBV-endemic areas, dietary staples are contaminated with aflatoxins, a potent human liver carcinogen. There is currently no vaccine against HCV. Therefore, research into reducing exposure to aflatoxins and effective low-cost treatments for chronic HBV and HCV carriers should be priorities. Similarly, research into cancer risk in individuals living with HIV is needed, particularly in relation to their susceptibility to other cancer-associated chronic infections. As breast cancer becomes the most common cancer in women and prostate cancer incidence likewise continues to increase in men, research into the most effective early detection approaches is vital, even in many low-income countries.
Implementation Research. Community-based or clinical cancer prevention trials are a valuable component in cancer control planning. However, the subsequent implementation and evaluation of prevention measures at the population level is often neglected. There may be many facilitators of and barriers to (eg, behavioral, cultural, system-based) successful integration of known prevention measures into health services. These factors need to be understood. In addition, the scale of effect of the intervention in practice may differ from that in a trial setting. These different aspects fall under the domain of implementation research, an area that merits a far greater priority globally. A key component of this area of research is an understanding of inequalities and disparities in relation to the effectiveness of cancer-control strategies. There are several relevant areas directly related to the priority interventions proposed above. For example, in some health service settings, it will be challenging to develop a delivery platform for HPV vaccination of adolescent girls (as opposed to young children or infants), and there may be cultural and social sensitivities with regard to preventing a cancer caused by a sexually transmitted infection. Similarly, important questions remain about barriers to participation in early detection of breast cancer and cervical cancer screening programs, including what factors influence whether women attend treatment after having an anomaly detected. It is vital that prevention is not only evidence based but also subsequently evaluated during implementation; there are opportunities in this regard for observational studies of public health interventions and health services research to pinpoint areas where improvements would have most impact. This type of research requires an interdisciplinary approach that involves social scientists, behavioral epidemiologists, and health service researchers to elucidate the personal, programmatic, and structural challenges to implementing cancer prevention.
Priorities for Cancer Research in Relation to the High-level Meeting
A number of research areas would provide vital evidence in establishing the most reliable evidence base for cancer control. Some that are particularly relevant to low- and middle-income countries are described below.
Improved Surveillance of Cancer Morbidity and Mortality and Prevalence of Major Risk Factors. Coverage of cause-of-death statistics is essential and is still lacking or incomplete in more than half the world's countries. To plan cancer services, governments need to know not only how many people are dying but how many will develop the disease and how many will live with it as cancer survivors. An understanding of temporal trends in the population prevalence of major cancer risk factors complements cancer surveillance to improve long-term cancer projections and planning. Cancer registries provide a platform for research, in addition to cancer statistics. They reveal geographical heterogeneity and temporal trends that generate etiological hypotheses. Registries are also vital in assessing the outcome of prevention-associated interventions, including community-randomized trials and planned public health interventions (eg, cervical cancer screening, early detection of breast cancer and HPV, or HBV vaccination). Population-based cancer registries are integral to both cancer control and research and as such should be a core component of any noncommunicable disease surveillance plan. Sadly, such registries are lacking or inadequate in many countries, especially in developing regions of the world. Sufficient knowledge and experience exist to provide support to countries to develop cancer registries that, with a modest level of sustained investment, would cover a defined region of a country, comprise a minimal dataset, and use open-source software (eg, CanReg5) to allow standard analyses and international comparisons. The IARC-led Global Initiative for Cancer Registry Development in Low- and Middle-Income Countries is an international cooperation designed to create regional centers of expertise in cancer registration, which in turn will provide the infrastructure to transform the coverage and quality of registration.
Cancer Etiology. The four shared noncommunicable disease risk factors require further research in relation to cancer. Examples of the research required are the need for more precision about the type and amount of physical exercise required to reduce cancer risk as well as a better understanding of the risks associated with specific nutritional and metabolic factors. Nevertheless, cancer also differs from other noncommunicable diseases in that risk factors for a number of major cancer sites remain poorly defined. Examples of common cancers where information on etiology is lacking include prostate cancer, colorectal cancer, leukemia, lymphoma, kidney cancer, and a substantial proportion of breast cancer. For other cancers, such as esophageal cancer, carcinogenic agents are known in developed countries but are less well understood in developing countries. Consequently, it is vital that research into the causes of cancer proceeds in parallel with research into prevention and implementation. Priorities for low- and middle-income countries should be focused on cancers that are common in the region and for which the risks cannot be easily inferred from previous research in high-income countries, either because investigations are lacking or because risk factors differ. In addition, exposure over the life course, including early in life, merits further study.
New knowledge about carcinogenic mechanisms and technologies to investigate biological changes subsequent to specific exposures offers important new opportunities to investigate cancer etiology. Progress in molecular cancer epidemiology is fundamental to moving forward in areas that have been refractory to yielding conclusive public health advice in recent years.
Prevention Research. Low-income countries have different cancer incidence patterns compared with high-income countries, notably in relation to cervical, liver, stomach, and HIV-associated cancers ( Table 1 ). As mentioned above, for some cancers, the challenge is to implement established interventions; for other cancers, the research priority should be to identify prevention strategies. For example, H. pylori infection is a well-established risk factor for stomach cancer, the second leading cause of cancer death worldwide, and yet optimal H. pylori eradication and its impact on stomach cancer incidence remain to be defined. Although HBV is associated with a majority of liver cancer cases worldwide, there are 350 million chronic HBV carriers whom HBV vaccination cannot help and in many HBV-endemic areas, dietary staples are contaminated with aflatoxins, a potent human liver carcinogen. There is currently no vaccine against HCV. Therefore, research into reducing exposure to aflatoxins and effective low-cost treatments for chronic HBV and HCV carriers should be priorities. Similarly, research into cancer risk in individuals living with HIV is needed, particularly in relation to their susceptibility to other cancer-associated chronic infections. As breast cancer becomes the most common cancer in women and prostate cancer incidence likewise continues to increase in men, research into the most effective early detection approaches is vital, even in many low-income countries.
Implementation Research. Community-based or clinical cancer prevention trials are a valuable component in cancer control planning. However, the subsequent implementation and evaluation of prevention measures at the population level is often neglected. There may be many facilitators of and barriers to (eg, behavioral, cultural, system-based) successful integration of known prevention measures into health services. These factors need to be understood. In addition, the scale of effect of the intervention in practice may differ from that in a trial setting. These different aspects fall under the domain of implementation research, an area that merits a far greater priority globally. A key component of this area of research is an understanding of inequalities and disparities in relation to the effectiveness of cancer-control strategies. There are several relevant areas directly related to the priority interventions proposed above. For example, in some health service settings, it will be challenging to develop a delivery platform for HPV vaccination of adolescent girls (as opposed to young children or infants), and there may be cultural and social sensitivities with regard to preventing a cancer caused by a sexually transmitted infection. Similarly, important questions remain about barriers to participation in early detection of breast cancer and cervical cancer screening programs, including what factors influence whether women attend treatment after having an anomaly detected. It is vital that prevention is not only evidence based but also subsequently evaluated during implementation; there are opportunities in this regard for observational studies of public health interventions and health services research to pinpoint areas where improvements would have most impact. This type of research requires an interdisciplinary approach that involves social scientists, behavioral epidemiologists, and health service researchers to elucidate the personal, programmatic, and structural challenges to implementing cancer prevention.