23 May 2016
In the early 1980’s Human Papillomavirus (HPV) was added to the list of viruses that can cause cancer when the German scientist, Harold zur Hausen, successfully demonstrated the presence of HPV DNA in the biopsy samples from women with cervical cancer. HPV was consistently observed in the majority of cervical cancer patients and was shown to transform normal cervical cells into cancer cells in laboratory studies. Over time, HPV’s causative role in cancer development was concluded. For this discovery, Harold zur Hausen won the Nobel Prize in Physiology or Medicine in 2008.
Interestingly, the rate of cervical cancer as a result of HPV has reduced significantly through time. This is mainly true among women in more developed countries owing to the frequent screening through regular Pap smear tests that can detect cells that appear to be HPV infected.
While the rate of HPV-caused cervical cancer has been decreasing, HPV is currently manifesting its cancer causing effects in the human oral (mouth and throat) cancer more than ever before. What do I mean by “more than ever before”? Well, agents such as tobacco and alcohol had always been the number one suspects when it came to oral cancer. Oncologists always knew that patients with oral cancer were likely heavy drinkers and/or smokers. In fact, it wasn’t until the late 1990s when doctors encountered an increased number of cases of oral cancer patients who were rather healthy individuals with no history of drinking or smoking.
It took many years of research to prove that the virus is actually responsible for 45%-90% of all cases of oral cancer depending on the where in the world it is taking place (World Health Organization, 2007).
While many head and neck specialists take charge of caring for patients with oral cancer, normally, they are the dentists who first notice the abnormalities in the oral cavity (in the form of white plaques or abnormalities inside the mouth and throat). The dentists would either report this to the patients and the primary caregivers or would take one further step by sending the samples for testing.
Unfortunately, in many instances, the cancer may progress greatly by the time the oral abnormalities get noted, the biopsies and testing get completed, and the results become available.
It is now known that there is a strong association between the HPV-caused oral cancer and the number of oral-sex partners the person has had. Although there has been HPV associated oral cancer detected in a small percentage of individuals who have not engaged in oral sex. It still remains to be understood whether deep kissing can also lead to the transfer of virus. The oral cancer formed in this manner can be considered almost a different disease than the one caused by heavy smoking and drinking.
HPV-caused oral cancer is typically treated like other squamous cell head and neck malignancies with radiation treatment and/or with chemotherapy. However, this type of oral cancer is thought to be easier to treat than oral cancer resulting from smoking or drinking. This may be due to the fact that the latter type may be due to susceptibility mutations that are affecting the patients’ DNA while the former is due to the HPV infection. This has led to the thought among specialists and researchers that HPV-caused oral cancer may need less toxic or less harsh chemotherapy regimens compared to cancers caused by other factors.
It is known that vaccination against HPV virus protects from most cases of cervical cancer; however, it is not well understood whether it acts similarly when it comes to oral cancer. While there are some implications for potential beneficial effects of the vaccine against oral cancer, further clinical investigation is required to determine the efficacy of the vaccine against this disease.
In general, there are a variety of HPV viral types and vaccination does not immunize against all papilloma viruses, only the most common ones. So far ~200 types have been identified and scientists are investigating ‘high-risk’ subtypes (those that are cancer-causing) and ‘low-risk’ types (those that lead to genital and oral warts but are not cancer-causing).
Repeated detection of high risk HPV types a critical risk factor for cancer development. When it comes to the detection of virus, there are limitations that come with accessing samples from the oral cavity. You can imagine how infeasible it is to routinely take biopsies from tonsils and throat of healthy individuals. Detection becomes particularly challenging when dealing with HPV types that tend to infect the back of the mouth.
The current challenge with the diagnosis and prognosis of oral cancer is to be able to detect the virus early on in the oral fluids such as saliva. This requires a very sensitive system. Scientists are currently working to build such a system that can improve early detection.