In the most general terms, cancer is a condition that results from an abnormality in the mechanisms that control cell division. The unregulated division of cells then leads to the formation of malignant tumors which go on to invade nearby structures and may even spread to other parts of the body via the lymphatic and circulatory systems.

Fortunately, our immune systems usually only tolerate the presence of our own cells, which means that cancerous cells can only invade the bodies which first produced them. If those cells were somehow transferred into the body of another person, that person’s immune system would quickly destroy them. This means that, generally speaking, cancer is not contagious.

A healthy diet, regular exercise, and a healthy lifestyle all help reduce the risk of cancer.

But in recent years researchers have discovered several biological oncogens. Although these can be highly contagious, controlling their spread opens up the possibility of preventing the cancers they cause.

Chen Chien-jen, an internationally renowned epidemiologist and a vice president of Academia Sinica, says that in February 2009 the International Agency for Research on Cancer, a division of the World Health Organization, gathered more than 30 top cancer scholars from around the world to draft a book on biological pathogens and cancer.

According to the book, the medical community has so far identified ten biological oncogens in humans: seven viruses, one bacterium, and two parasites. These can be further categorized as either direct or indirect oncogens. The direct oncogens include the human T-lymphotropic virus (HTLV), which carries oncogenic genes, Epstein-Barr virus (EB), which possesses genes that halt cellular apoptosis, and human papilloma virus (HPV), which disables tumor suppressor genes.

Indirect oncongens include the hepatitis B and C viruses, which cause inflammation in the liver, and the bacterium Helicobactor pylori, which causes inflammation in the stomach. This inflammation can eventually give rise to cancer.

The Liver Disease Prevention and Treatment Research Foundation has long offered free hepatitis screening to residents of Taiwan’s more remote areas. The photo shows a screening session on ­Penghu in 1999.

Of the ten oncogenic pathogens, it is Epstein-Barr virus that most urgently needs investigation. A human herpes­virus, EB is highly contagious, transmitted via saliva, and widespread. In fact, it is estimated that more than 90% of adults worldwide have been infected with it at some time in their lives.

Most infected people don’t become obviously ill, though a few will exhibit fever and upper respiratory symptoms such as a sore throat or inflamed tonsils. Though the body quickly produces antibodies, the virus persists in our B cells (a type of lymphocyte) and in our noses and throats for the rest of our lives.

The medical community believes that there may be a link between EB and nasopharyngeal cancer. Its reasoning is straightforward: nasopharyngeal tumors typically contain large quantities of EB genes and proteins, and nasopharyngeal cancer patients tend to have much higher than normal levels of EB antibodies in their blood.

Chen Chien­-jen therefore led an investigation into whether the spike in antibodies initiated the tumor, or was a response to the tumor. He and his team studied 10,000 male participants for 16 years in six townships in Hsin­chu, Yi­lan, and Ping­tung, ultimately finding that participants who had high levels of the EB antibody in their blood were six times more likely to develop nasopharyngeal cancer than those with low levels.

Given this link, Chen says that the concentration of EB antibodies in blood and the EB content of epithelial cells in the nasopharyngeal region hold promise as a mechanism for the early detection of nasopharyngeal cancer.

A healthy diet, regular exercise, and a healthy lifestyle all help reduce the risk of cancer.

But if more than 90% of us have been exposed to EB, why do so few of us go on to develop nasopharyngeal cancer? Similarly, if nearly 80% of women recover completely from HPV infections, why do 10% remain infected and 1% develop cervical cancer?

Chen says that the pathogen, the host, and the host’s living environment all play a role.

In the case of the pathogen, the risk of developing cancer is closely linked to the genotype and quantity of the pathogen to which the host has been exposed. For example, in the case of hepatitis B, the C genotype is twice as likely to cause cancer as the B genotype.

In the case of the host, the individual’s gender, age, genetic makeup and family history are all factors. For example, men have a far higher incidence of liver cancer than women.

A host’s genetic makeup is even more critical. For example, individuals whose ancestry lies in the southeast coastal region of China have a much higher than average incidence of nasopharyngeal cancer. This applies even among those who have emigrated to Southeast Asia, Europe, or the United States.

A host’s lifestyle is also important. For example, liver cancer caused by viral hepatitis progresses more rapidly in people who smoke or are obese, and those who eat foods containing nitros­amines (e.g. smoked meats and seafoods), or who have long-term exposure to certain chemical agents such as formalin, are much more likely to acquire EB-induced nasopharyngeal cancer.

Imaging showing the spread of cancer cells into the lungs of rats.

Though the risk of cancers caused by viruses is high, such cancers have a known pathogenesis that allows them to be prevented.

Vaccination, which results in the production of antibodies to the oncogenic virus, is the most effective means of prevention. Taiwan’s world-renowned war on hepatitis B is an example of just how well this can work.

Hepatitis B is the primary cause of liver cancer. Transmission is perinatal or through exposure to infected bodily fluids. According to the WHO, there are currently some 240 million chronic carriers around the world.

In the 1980s, Sung Juei-low, an academician with the Academia Sinica, pushed for a program to halt perinatal transmission in Taiwan, which led to our introduction of the world’s first comprehensive hepatitis B vaccination program for newborns in July 1986.

The program has been phenomenally successful. By 1996, it had reduced our rate of hepatitis B infection from its world-topping level of 15–20% of our population to less than 1% among our children.

Chen Ding-shinn, a Sung protégé and fellow academician, predicts that the incidence of liver cancer among Taiwanese adults will likewise fall sharply by 2034, 50 years after the initiation of the inoculation program.

Cervical cancer, which is the second leading cause of death among Taiwanese women, has had a vaccination of its own since 2006.

A variety of tests and examinations, from endoscopies to blood tests, can detect the presence of Helicobactor pylori, a bacterium that can cause stomach cancer.

Regular examinations are another crucial weapon in the fight to prevent cancer.

Take cervical cancer, for example. For all that HPV is the principal cause of cervical cancer, the current vaccines only protect against types 16 and 18, the most oncogenically potent varieties. In other words, the vaccine doesn’t provide complete protection, and women still need to undergo Papanicolaou testing (Pap smears) on a regular basis.

Taiwan has been promoting annual Pap smears for women over the age of 30 since 1995. An estimated 70% of women 30–69 years of age are currently thought to have had a Pap smear within the last three years. While this is below the 85% figure for Europe and the US, there have nonetheless been demonstrable declines in cervical cancer incidence and mortality rates in Taiwan. Nowadays, approximately 600 Taiwanese women lose their lives to cervical cancer every year, a figure that is down by a third from a decade ago.

In an effort to promote early detection among the many women who refuse gynecological exams and Pap smears, the Health Promotion Administration has introduced a “self smear” service for women who haven’t had a Pap smear for six years. The service allows women to swab their cervix themselves, then send the resulting sample in for examination.

Helicobacter pylori, the only bacterial oncogen identified so far, has been demonstrated to be the cause of as many as 80–90% of stomach cancers. The bacteria can be transmitted via the oro­fecal route (by consuming contaminated food or drink), as well as through the shared use of eating utensils, shared foods and beverages, and kissing. As a result, the infection of an individual usually means the infection of their entire family.

As H. pylori infections progress, they cause chronic inflammation of the stomach. In severe cases, they can lead to stomach or duodenal ulcers, which can worsen and ultimately become cancerous.

The Matsu islands have Taiwan’s highest rate of H. pylori infection. Seeking to reduce the incidence of stomach cancer in the islands, Wu Ming-­shiang, a professor with the Department of Internal Medicine at National Taiwan University College of Medicine, and his team initiated a bacterial eradication program in 1999. The program ran for more than a decade, focusing on mass screening, long-term tracking, and proactive treatment of infection. It has been a tremendous success, leading to a 30% decline in Matsu’s incidence of stomach cancer.

Last year, Wu’s research team introduced a new treatment for H. pylori infection that combines a proton-pump inhibitor (which reduces acid levels in the stomach) with three different antibiotics. Administered in two stages, the treatment has a 94% success rate.

Years of hard work by the medical community have taken their toll on stomach cancer. Once the third most deadly cancer in Taiwan, it now ranks only sixth.

Advances in medicine have brought us to a turning point in the effort to prevent and treat cancers caused by biological pathogens. With vaccinations, regular exams, healthier diets and lifestyle changes, reining in the cancer crisis may no longer be beyond reach.