Improved screening and early-detection efforts, combined with decreases in risk factors like smoking, are reducing the incidence and mortality rates from several common forms of cancer in many high-income countries (HICs), but death rates are escalating in low- and middle-income countries (LMICs), according to a study published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.
"The rates of many cancers are being brought under control in Western countries through decreasing prevalence of known risk factors, early detection, and improved treatment," said Lindsey A. Torre, MSPH, epidemiologist at the American Cancer Society and lead author of the study. "In contrast, rates for cancers such as lung, breast, and colorectum are now rising in many LMICs due to increases in risk factors typical of Western countries, such as smoking, excess body weight, physical inactivity, and changing reproductive patterns."
Torre and colleagues analyzed incidence and mortality data for the years 2003-2007 from the International Agency for Research on Cancer (IARC) CancerMondial database, which includes incidence data through 2007 from Cancer Incidence in Five Continents, a collaboration between the IARC and the International Association of Cancer Registries, and mortality data through 2012 from the WHO Cancer Mortality database. Study data reflect 50 countries selected to represent various regions of the world.
Worldwide, an estimated 14.1 million new cancer cases and 8.2 million cancer deaths occurred in 2012, the authors said. Incidence and mortality rates varied greatly from nation to nation. In their report, the authors noted developments across eight major kinds of cancer, which account for 60 percent of total global cases and deaths. Some highlights:
"In many of the lower- and middle-income countries, mammography is just not available," Torre said. "Meanwhile, these countries are experiencing changing lifestyles, including excess body weight, having fewer children, and breastfeeding for a shorter duration. These are all known risk factors."
In the United States, liver cancer mortality rates have increased. Researchers believe the increase is linked to hepatitis C as a result of contaminated blood or medical equipment, or injection drug abuse during the 1960s and 1970s. The rise in obesity and type 2 diabetes may also play a part, the researchers wrote.
Torre said that the most significant limitation of the study was the variation in reporting standards from one country to the next. For example, she said some nations do not require deaths to be registered, so the mortality data may not be fully representative. Also, data in many countries were collected only in urban centers, which means that cancer incidence and mortality across a whole country's population may not be accurately reflected.
"Despite the limitations, it's fascinating to be able to compare data from all over the world," Torre said. "This study gives us important clues about the epidemiology of cancer and gives us some ideas about what we could further investigate to improve global public health."
This study was sponsored by the American Cancer Society. Torre declares no conflicts of interest.
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