Opinion: Preventing cancer the easy way

Preventing cancer is always a better option than trying cure it, but while we might often think of this as having to involve a major change in behavior or a shift in public health policies — and sometimes even pre-emptive surgery — for some cancers there is another much easier way. At least 1 in 10 cancers can be prevented using one of the most widely available medical interventions — vaccines.

This is possible because a large number of cancer cases are not caused by risk factors we traditionally associate with noncommunicable diseases — such as obesity, tobacco use, or alcohol consumption — but can be triggered by infectious agents. In low- and middle-income countries this is already true for as many as 1 in 4 cancer cases, while in sub-Saharan Africa it’s more than 1 in 3, and typically occurs in younger people. With this in mind, it is important that we recognize the frontline role that immunization can play as we take on the growing threat of NCDs.

The good news is that more than 90 percent of these cancers are caused by just four pathogens, and we already have safe and highly effective vaccines for two of them: Hepatitis B virus and human papillomavirus, or HPV.

Preventing the hepatitis B virus

The hepatitis B virus causes between 60-80 percent of primary liver cancer cases, which is the leading cause of cancer deaths worldwide. Liver cancer is a particularly aggressive form of cancer with limited treatment options, and the cost or lack of access to treatment in low-income countries means that it often kills within months of diagnosis.

Since a vaccine was first developed in the 1980s, we have seen a more than threefold drop in the global hepatitis B infection rate in children and a noticeable drop in liver cancer cases. For example, in China, around 10 percent of the population were chronic carriers of the virus at the end of the last century. Gavi, the Vaccine Alliance began to work with the government of China in 2002 to increase coverage with the hepatitis B vaccine. By 2010, less than 1 percent of children under 5 were chronic carriers of the disease. Today, we are helping to protect 60 percent of the world’s children living in low-income countries against hepatitis B through the 5-in-1 pentavalent vaccine.

Preventing HPV virus

The HPV vaccine is a more recent addition to our repertoire. HPV is a contributing factor in almost all cases of cervical cancer, which is the most prevalent cancer in many low-income countries. More than 260,000 women a year die from the disease, 85 percent of whom live in developing countries.

A vaccine against several key cancer-causing strains of the virus became available in 2006. Studies in several countries have shown a dramatic reduction in the rate of HPV infection. Recent figures released by the United Kingdom show an 86 percent drop since 2010 in the infection rate among young women. Gavi started providing support for the HPV vaccine in 2013, and we have since supported demonstration projects in 28 countries and helped eight countries to introduce the vaccine into their routine vaccination schedule, including four in sub-Saharan Africa. Two more Gavi-supported countries are expected to follow suit by the end of the year.

What next?

In addition to hepatitis B and HPV, research into developing vaccines against the other key cancer-causing infectious agents is ongoing. Infection with Helicobacter pylori can predispose people to developing stomach cancer, which is the third most common cause of cancer-related death. A proof-of-concept has shown that vaccination can protect children from H. pylori infection and a vaccine is currently going through early stage clinical trials.

Unfortunately, despite the large global burden of the disease, the development of a vaccine against H. pylori is not a priority for major pharmaceutical companies — because LMICs bear the brunt of the disease burden, the financial incentive to develop such a vaccine is low.

The bottleneck for developing a vaccine against another cause of liver cancer — hepatitis C — falls at an even earlier stage in the process, with the nature of the virus itself making vaccine development challenging. Hepatitis C coat proteins, which are the part of the virus that our immune system can easily recognize, are highly variable. This means that the antibodies in the blood of a vaccinated individual will not recognize hepatitis C if the person is infected by a strain that looks very different from the strain they are vaccinated against.

Vaccination has already enabled us to eradicate smallpox and has brought us close to doing the same with polio. It has reduced measles cases worldwide by 90 percent and brought outbreaks across the world under control. Now, they could even help us prevent devastating NCDs such as cancers. Such a simple, cost-effective weapon against this complex, often poorly understood group of diseases is an opportunity we cannot afford to pass up.

With 1.4 million cancer cases in developing countries every year caused by infections, further investment is crucial to ensure that vaccines against other cancer-causing infectious pathogens are developed and brought to market. The far-reaching impact on people, communities, and economies in the world’s poorest countries would see this investment returned countless times over.

For more coverage of NCDs, visit the Taking the Pulse series here.