Wednesday, April 4, 2012

Human Papillomaviruses and Oral Cancer

For many decades smoking and alcohol abuse were the major risk factors for oral cancer. In contrast, smokeless tobacco use, while commonly misperceived as a common cause, has played virtually no role. Now, there is emerging scientific evidence that human papillomaviruses (HPVs), which are recognized to cause cervical cancer in women, may cause oral cancer. A new study by Anil K. Chaturvedi, from the National Cancer Institute, and investigators from five other institutions, provides evidence that HPVs have played an increasing role in some cancers of the mouth and pharynx (abstract here).

Chaturvedi and colleagues looked for HPVs in cancers of the base of tongue, tonsil and oropharynx collected by cancer registries in Hawaii, Iowa and Los Angeles from 1984 to 2004. They found that HPVs were present in only 16% of tumors during the 1980s, but by 2004 over 70% of these tumors were HPV positive.

Chaturvedi and colleagues concluded that “HPV-positive [oropharyngeal cancers] will likely constitute a majority of all head and neck cancers in the United States in the next 20 years,…” and “by 2020, the number of HPV-positive [oropharyngeal cancers] is expected to surpass the number of cervical cancers, the focus of prophylactic HPV vaccination.” The investigators argued for “evaluation of the efficacy of vaccination to prevent oral HPV infections, particularly given the unavailability of screening for [orophyyngeal cancers].”

It is important to note that Chaturvedi only looked at a subset of mouth and throat cancers. Oral cancer also occurs under and on the sides of the tongue, and these tumors are less likely to be HPV positive.

The authors note that “[oropharyngeal cancer] incidence increased from 1973 to 2004 in the United States, particularly among young individuals (< 60 years of age), men, and whites.” However, they didn’t provide the perspective that oral cancer is a very rare disease. I have analyzed the National Cancer Institute’s cancer registry; in 2003, there were only 10,400 cases of oral cancer in the United States, and there were 12,200 cases of pharynx-throat cancer (reference here). I wrote that “[i]f every oral cancer was detected by one of the 128,000 general dentists in the United States, then on average each dentist would make one diagnosis every 12 years.”

The authors classify the cancers into HPV positive and negative, and they write that “the declining incidence of HPV-negative [oropharyngeal cancers] parallels declines in smoking in the United States.” However, very little is known about the interaction between HPV and smoking or alcohol use.

Chaturvedi and colleagues make a good case that the increasing number of HPV-positive oropharyngeal cancers “argues for evaluation of the efficacy of vaccination to prevent oral HPV infections...” Vaccination has the potential to reduce the incidence of cervical cancer among women, and further to reduce HPV infections among both women and men.

If vaccination is a no brainer for cervical cancer and for HPV-positive oropharyngeal cancer, what about cancer caused by smoking? The epidemiologic evidence documents that smokeless tobacco and e-cigarettes have the potential to immunize smokers against these and other deadly illnesses.

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