Perhaps we should broaden our horizons a bit beyond just Smoking and HPV.

During my search to know, I found this on www.canceranswers.com and have often notice similar info elsewhere.

Like any cancer, the exact reason why one person gets oropharynx cancer and another does not
remains unknown. However, several"risk factors" have been shown to be be much more likely to be
present in mouth cancer patients:

1. Tobacco Usage--
This is the single strongest risk factor for developing cancers of the head and
neck, and especially mouth, esophagus, and oropharynx. Any form of tobacco taken through the
mouth, whether smoked or chewed, increases the risk over time. It often takes several decades
of use to get cancer but children who use chewing tobacco (often to emulate famous baseball
players) have gotten mouth cancer. The more tobacco that is used, for a longer period of time,
the higher the chance to get mouth cancer. Likewise, when use is stopped, the risk declines
almost to normal over a 5 to 10 year period.

2. Alcohol Usage--
Is the next strongest risk factor after tobacco. Occasional wine or beer may
raise risk very slightly, if at all, but frequent use of strong drinks like whiskey will increase cancer
risk to the mouth, throat, esophagus (food pipe), stomach and pancreas.
Furthermore,combining alcohol with tobacco will have a "super additive" effect to greatly
increase cancer risk for all of these areas. This means that the risk is much more than twice as
high as for using either tobacco or alcohol alone. Like tobacco, people who stop frequent drinking
will gradually lower their cancer risk to nearly that of non-drinkers.

3. Poor Oral Hygiene--
The more unclean the mouth and throat are, the more it is subject to
constant irritation from grime. Each teaspoon of saliva contains about one billion bacteria, which
are making waste products which cling to teeth and tonsils ("plaque"). This allows gum disease
(pyorrhea) to lead to subsequent tooth loss. Although plaque itself is not show to cause cancer, it
helps other chemicals (like in smoke) to stick in the mouth and throat, irritate it, and stimulate the
cells to divide. The more cells divide, the more chance one of them will become cancerous. That
is why the common thread of many risk factors is irritation, leading to lots of cell division.

4. Ill-Fitting Dentures
irritate the gum lining ("gingiva") and trap debris. This can lead to tongue
cancers over time.

5. Betel-Nut Chewing
in Indian populations is strongly associated with tooth loss, mouth and throat
cancer, again the common factor is prolonged irritation.

6. Infections
such as syphilis and some viruses can lead to cancer over time, these cause throat
sores which heal poorly. The constant attempt to heal leads to chronic cell division and thus
more chance for cancer. Viruses can also get into the mouth cells themselves and change the
genes in them to form a cancer cell. This elaborate process is called "oncogene activation".

7. Lowered Immunity
such as from AIDS or transplant anti-rejection drugs will increase the risk for
many cancers, including those of the "aero-digestive tract" (i.e. the area from the nose and
mouth to the lungs and stomach). This will be especially important in combination with the other
risk factors noted above.

8. Precancerous "Plaques"
can develop in the mouth and throat, from chronic irritation. These
may be white in color ("leukoplakia") or red ("erythroplasia") and may or may not become
cancerous. They must be monitored closely.

9. History
of Cancer of the aero-digestive tract can mean as much as 5% chance of a separate
simultaneous cancer, and a 25% chance of developing another cancer in this area over time
(especially if risks like smoking are continued).

A cancer must grow to 1 billion cells to be just 1 cm. (about 1/2) across, so a very early cancer will
have no symptoms and likely go undetected.