How Cancer Mortality Rates Influence Life Expectancy

Cancer


Cancer encompasses a range of diseases with varying mortality rates. A recent study has shown how cancer mortality rates have changed and influenced life expectancy over 30 years and have uncovered discrepancies in cancer control efforts between different populations.

Cancer is predicted to become the primary cause of global morbidity and mortality, surpassing cardiovascular disease (CVD). There are distinct differences in cancer mortality rates between and within countries, and between different types of cancers. Although mortality rates are generally declining in most highly developed countries thanks to effective prevention and early detection strategies, treatment is only effective for certain types of cancers, making it difficult to determine the impact of cancer on life expectancy and how well it is being controlled.

A recent study in the British Medical Journal analyzed how cancer mortality influenced the life expectancy of individuals between 1981 and 2010 using a retrospective demographic analysis. Information on individuals aged 40-84 years from 52 populations was obtained from the World Health Organization mortality database. Population counts were obtained from the United Nations World Population Prospects. Individuals were divided into two groups based on the Human Development Index (HDI), an indicator of national prosperity: Group 1 (very high HDI) and Group 2 (medium and high HDI). Life expectancy (LE) was calculated for each population and sex. Changes in LE between 1981-1985 and 2006-2010 due to cancers, CVD and other causes of death were then estimated.

LE increased during the 30-year period, with greater increases seen in Group 1 (3.7 vs 2.5 years; male vs female) compared to Group 2 (1.1 vs 1.4 years; male vs female). This corresponded to a decrease in overall mortality rates, approximately half of which were due to declining CVD mortality rates (60%, Group1; 50%, Group 2). Declining cancer mortality rates were also observed, with greater decreases in Group 1 (20% vs 15%; male vs female) compared to Group 2 (4% vs 5%; male vs female). Stomach cancer was the only cancer where mortality rates decreased in both sexes (60% vs 45%; Groups 1 vs 2). Declining lung cancer mortality rates (26% vs 13%; Groups 1 vs 2) had the largest impact on LE in men. In contrast, lung cancer mortality increased in women (40% vs 12%; Groups 1 vs 2), which may reflect the increasing empowerment of women in wealthier countries. Breast cancer mortality decreased in women in Group 1 but increased in Group 2. A similar result was found with prostate cancer mortality in men.

Overall, this study shows that global declines in CVD and cancer mortality rates contribute to increased life expectancies. The contribution from cancer mortality rates is much smaller, possibly due to the multifaceted and unpredictable nature of cancer, and the fact that many cancers remain untreatable. Cancer mortality rates vary depending on sex and population, possibly because more prosperous populations have better access to the resources required to combat cancer and greater equality between sexes. This indicates that provision of much-needed resources and implementation of effective cancer intervention and management programs is vital for reducing cancer mortality rates in less prosperous countries.

Written by Natasha Tetlow, PhD

Cao B, Bray F, Beltran-Sanchez H, Ginsburg O, Soneji S, Soerjomataram I. Benchmarking life expectancy and cancer mortality: global comparison with cardiovascular disease 1981-2010. BMJ. 2017;357:j2765. Available at: doi: 10.1136/bmj.j2765.



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