Abstract PL02-01: Global trends in cancer incidence: priorities for prevention
Authors: Thun Michael , DeLancey John Oliver , Center Melissa , Jemal Ahmedin 
Published: May 2012

PL02-01

More than 12 million new cancer cases and 7.6 million deaths from cancer are estimated to have occurred worldwide in 2007, making cancer the third leading cause of death after cardiovascular and infectious/parasitic diseases. If current trends continue, the number of cancer deaths worldwide is projected to reach 11.5 million deaths in 2030, nearly double the estimated 6 million that occurred in 1990. Moreover, the cancer burden is no longer confined predominantly to the industrialized, wealthy countries, but is shifting to low and medium resource countries. The percentage of all cases that occur in low and middle income countries has increased from approximately half (51%) in 1975 to 55% in 2007 and is projected to reach 61% by 2030.

There are three principal factors that drive global cancer trends: (1) the growth and aging of populations; (2) the entrenchment of chronic disease risk factors (cigarette smoking, Western diet, and physical inactivity) in developing countries; and (3) the much slower decline in cancers related to infectious etiologies in low than in high resource countries. These factors have very different effects on estimates of the cancer burden. Population growth and aging are largely responsible for the increasing number of cancer cases and deaths and for the shift in the proportionate contribution from high to medium and low resource countries. The other two factors have opposite effects on different types of cancer. The geographic shift in the prevalence of modifiable chronic disease risk factors has caused an increase in incidence and death rates from cancers of the lung, breast, and colorectum. In many developing countries, this largely cancels out small decreases in incidence and death rates for cancers of the stomach, liver, and uterine cervix, changing the composition of the cancer burden without a large impact on overall cancer rates.

Tobacco use alone causes more cancer cases and deaths than any other risk factor. The top priorities for prevention, therefore, require greatly strengthened global efforts in tobacco control, combined with regionally focused initiatives to prevent the chronic infections that cause more than 20% of cancer deaths worldwide. Effective tobacco control measures exist but are not consistently implemented. They include policy interventions that increase tobacco taxes, prevent smuggling, ban direct and indirect tobacco advertising, establish smoke-free public places, provide cessation services to help smokers quit, and employ hard-hitting antitobacco advertising campaigns to change social norms about tobacco use.

Liver cancer is the most common vaccine-preventable cancer, and is essentially tied with colorectal cancer as the third leading cause of cancer death world wide. More than 80% of cases occur in sub-Saharan Africa and Eastern Asia; 50% of the cases occur in China alone. Hepatitis B virus is estimated to account for about half all hepatocellular cancer deaths globally. While there is currently no vaccine for hepatitis C virus, which is also a risk factor for hepatocellular cancer, a safe and effective vaccine against Hepatitis B has been available since 1982. Vaccination with this vaccine has been shown to be the most cost-effective strategy to reduce liver cancer. Effective vaccination programs could avert at least 300,000 deaths per year. The cost of the vaccine has been reduced from $100 to $1 (for three doses of treatment) through the efforts of the Global Alliance for Vaccines and Immunization. Over three quarters of WHO member states have introduced hepatitis B vaccine into routine infant immunization schedules, although in many places it is difficult to deliver the vaccine within 24 hours of birth. Vaccine delivery is particularly challenging in high risk, low resource areas of Africa.

Cervical cancer is the second most common cancer among women worldwide, with an estimated 555,000 new cases and 310,000 deaths in 2007. Although the age-standardized incidence rate is considerably lower in Asia than in Central America, Asia accounts for more than half of the world’s cervical cancer cases and deaths because of its immense population. Effective vaccines against HPV infection are too costly to be available in high risk areas. Consequently, negotiations for tiered pricing must reduce the cost from about $360 per woman and identify alternative sources of funding if the vaccine is to be made available in the areas of greatest need in the next 10-20 years. In the meantime, promotion of condom use, and visual screening using acetic acid or DNA testing for HPV provide important but suboptimal alternatives. Cytology based (PAP) screening is not affordable in low income settings.

Although incidence and death rates from stomach cancer have been falling worldwide, even in high risk countries, stomach cancer remains second only to lung cancer as the leading cause of cancer deaths. Stomach cancer accounted for more than one million estimated cases and 800,230 deaths in 2007, up from 933,937 incident cases and 700,349 deaths in 2002, with the number of cases and deaths continuing to increase globally because of population growth and aging. The eradication of Helicobacter pylori in asymptomatic carriers has been proposed as a potential method to prevent stomach cancer. Trials of the efficacy of this approach in preventing the development of atrophic gastritis should be conducted in high risk areas. However, this approach does not preclude the existing practice of surveillance of gastric cancer in high-risk populations.

In summary, preventive measures offer the only feasible approach to slow and ultimately reverse the global increase in cancer occurrence and its disproportionate burden on countries that are least able to afford its adverse health and economic consequences.

Citation Information: Cancer Prev Res 2008;1(7 Suppl):PL02-01.