Although smoking is clearly a major risk factor for lung cancer development, pathogenic viruses acquired from consumption of red meat may be a synergistic causative factor, argued Harald Zur Hausen, MD, in the keynote address at the International Association for the Study of Lung Cancer (IASLC) 17th Annual World Conference on Lung Cancer in Austria.
Dr Hausen, who was awarded the 2008 Nobel Prize in Medicine for his discovery that human papillomavirus (HPV) can cause cervical cancer, discussed the risk factors for the 20% to 25% of lung cancer developed by non-smokers, and asked whether smoking is a sole causative factor or if it interacts with genetic or epigenetic gene modifications.
He suggested that oncogenic viruses could also play a role in lung cancer. “A well-known example that exists is recurrent laryngeal papillomatosis,” he said. “We do know that rare cases of bronchial cancer have been found that are due to HPV11 or HPV6 infections.”
Without exception, oncogenic viruses require additional genetic or epigenetic modifications in order to turn latently infected cells malignant, he said. In healthy individuals who are infected with an oncovirus, various cellular signaling cascades effectively inhibit oncogene expression. The failure of any one of these cascades, however, will allow the expression of viral oncogenes, leading to invasive growth and metastases.
Epidemiological surveys have indicated an increased risk of lung and oropharyngeal cancers among butchers and slaughterhouse workers, who are regularly exposed to aerosols originating from slaughtered animals. This may point to an infectious cause that is inhaled, said Dr Hausen.
Furthermore, a number of human pathogenic viruses induce carcinomas upon inoculation into animals, and there may be animal pathogenic viruses that could be carcinogenic to humans.
Dr Hausen also noted that lung cancer incidence is not always correlated to high rates of smoking. In particular, in spite of a high rate of smoking in India, lung cancer is not very prevalent. Colon cancer is apparently linked to beef consumption, said Dr Hausen, and he suggested there may be a similar correlation to lung cancer. “In India there is one type of meat that is not being consumed, and that is beef,” he said. “India has the lowest rate of colon cancer globally, and a relatively low rate of lung cancer as well.”
Conversely, certain environmental factors may contribute a protective effect against cancer development, and Dr Hausen discussed the protective effects of prolonged breast feeding in particular. He noted 1 study that found a 45% reduction in lung cancer risk for lactose-intolerant people who had had prolonged breast feeding as children. He said that this may also indicate a major risk of lung cancer originates in systemic infection by a bovine milk or meat factor.
Ultimately, smoking cessation remains paramount to preventing lung cancer mortality, said Dr Hausen, but research should continue to search for synergistic factors, such as infections or diet, that could lead to a new concept for lung cancer prevention.
- Hausen HZ. Is smoking a sole factor in lung cancer development? Keynote lecture presented at: 17th World Conference on Lung Cancer; December 2016; Vienna, Austria.