I think the following taken from Rodu and Godshall's Tobacco harm reduction: an alternative cessation strategy for inveterate smokers answers this in some detail. See the original for further reading or for details on the research behind the report.
Oral leukoplakia is an ominous sounding term used frequently in discussions about ST use. The term literally means "white plaque," and it is used to describe areas of the mouth lining that become thickened by ST use or smoking. The World Health Organization has determined that leukoplakias resulting from ST use are considerably different from those resulting from smoking. The distinctions are based on the frequency of occurrence, the location in the mouth, and how often these leukoplakias result in mouth cancer.
The condition is rare, occurring in less than 1% of the general population, primarily in long-time smokers 40 to 60 years old. Smoking-related leukoplakias most commonly involve the undersurface of the tongue and throat area, locations that account for 75% of oral cancer in the U.S..
Oral leukoplakias occur in up to 60% of ST users, within 6 months to 3 years of starting ST use. They primarily occur at the site of ST use and are largely a result of local irritation. The frequency of appearance depends on the type of ST that is used. Moist snuff, which is more alkaline than chewing tobacco, more often leads to leukoplakia. However, moist snuff in pre-portioned pouches causes fewer cases of leukoplakia than does the loose form.
There are distinct differences in how often ST and smoking leukoplakias show pre-cancerous changes called dysplasia. Dysplasia is seen infrequently in ST leukoplakias (less than 3%). Furthermore, even when dysplasia is present in ST leukoplakia, it usually is found in earlier stages than in leukoplakias due to smoking, where it is seen in about 20% of cases.
ST leukoplakias only rarely progress to cancer. For example, one prospective study found no case of cancer in 1,550 ST users with leukoplakia who were followed for 10 years, and a second study reported no case of oral cancer among 500 regular ST users followed for six years. A retrospective study of 200,000 male snuff users in Sweden found only one case of oral cancer per year, an extremely low frequency. In comparison, a follow-up study reported that 17% of smoking leukoplakias transformed into cancer within seven years.
In conclusion, oral leukoplakia occurs commonly in ST users, but it primarily represents irritation and only very rarely progresses to oral cancer.
To restate the conclusion from our answer to a similar query (see above): oral leukoplakia occurs commonly in ST users, but it primarily represents irritation and only very rarely progresses to oral cancer. The key thing to keep in mind is this: Modern smokeless tobacco does not appear to cause oral cancer, at least not enough that we can measure the increase, so it is impossible for leukoplakia (which is fairly common among smokeless tobacco users) to represent a cancer risk. If it did, then there would be a noticeable increase in cancer -- but there is not a noticeable increase in cancer. It is pretty simple once you think about it. The people who put out the information you cite either do not think about it, or are intentionally providing what they know to misleading claims.
The answer to the previous posting will give you details and a link to follow for more information. By the way, leukoplakia basically means a white patch, and keratosis simply means a toughening of the tissue. These are both natural responses to local irritation. In smokeless tobacco users, leukoplakia almost always disappear soon after quitting or changing the place where the produce is held. If you find you have a localized irritation when you use smokeless tobacco, especially soon after you switch from smoking, and you want to get rid of it, use the product at a different spot in your mouth for a while. Definitely do not switch to smoking, which is pretty much the worst thing you can do for your oral health.
Your question gets rather far from the purpose of this website. Methods for earlier detection of oral cancer are described in publications that specialize in such matters, and we defer to them on the specific point. We will note the error you make in framing your question that does relate to the purpose of this website: Exclusive ST users, just like everyone else who does not smoke, have such a small chance of getting oral cancer that it should be far down your list of worries. Smokers have a much greater chance, but it is still rather small. Moreover, oral cancer is a geriatric disease, and usually follows about 50 years of smoking. (The handful of cases of oral cancer in young people are an interesting mystery, since they are not associated with smoking or drinking -- the known risk factors -- but they are a different story.) So, basically, questions like "Do you even lessen your odds further by moving the dip around?" are based on the premise that ST causes oral cancer to a measurable degree, which the science shows is not the case. As you will find recounted in detail in our website (and further under the Oral Lesions discussion in this forum), there is ample "concrete data" on this point. Since holding the dip in the same place always creates either zero risk or such small risk it cannot be measured, moving it around would be an attempt to go from no additional risk to even less than that, which obviously does not make sense. If you are really so inclined to worry about signs of cancer and you are younger than about 50, keep an eye on your skin. If you are 50 or older, consider colonoscopy and other screening tests. Beyond that, you are better off spending the time exercising to prevent disease rather than searching your body for disease. And, of course, DON'T SMOKE!
If you are concerned about a sore in your mouth, have it checked by a professional. And if you happen to be a smokeless tobacco user, and continue to worry about possible health effects, why not just quit?
The public education parts of this website are directed toward smokers who have not quit smoking. The goal is that if someone has tried to quit using nicotine and failed, or if they are not inclined to quit using it, we want to let them know that they can use nicotine with very low health risks instead of facing the huge risks from smoking. It should be obvious that we, along with everyone else working in public health, do not oppose quitting. But we, along with anyone in public health who really cares about people and respects health ethics, think that if you do not quit nicotine you deserve an option other than being quite likely to die from it. Public health takes the same attitude toward driving (it is dangerous but since you will not stop, at least put on seat belts).
We do not want to trivialize any person’s tragedy, but we want to make sure that these stories are not used to mislead people about the science. Oral cancer is primarily a geriatric disease, but a small number of cases occur in young people. It would be comforting to attribute these cases to something people could stop doing, but the facts do not support this and wishful thinking does not help. The cases in young people are not associated with the cause of 3/4 of all oral cancers in North America (smoking), or any other known factor. Of course, coincidence happens: With a few hundred such cases per year, some of the people smoke, some of them use smokeless tobacco, some of them have red hair, some of them drink a lot of coffee, etc., but that does not mean that any one of these caused the cancers in those people. So even if Sean Marsee had been a smoker and was being used as a poster boy for the dangers of smoking, we would have to say it was inappropriate even though smoking does cause most oral cancer (in much older people
While we cannot teach a full introductory statistics class in this post (there are some good books that are easy reads if you want), consider this: Take a pair of white dice and a red die and roll all three, record the results, and repeat it 1200 times (hint: do it in a spreadsheet rather than acutally using dice). Each 6 on the red die represents a case of oral cancer in a young person (roughly how many occur in North America per year). Each time the white dice added to 12, that represents someone who uses smokeless tobacco (roughly the prevalence of use in young North Americans). Did the 12s cause the 6s in those cases? Obviously not. And yet there are probably about 6 occurrences of this combination. That represents about 6 young people per year who both use smokeless tobacco and get oral cancer, purely by coincidence. The fact that we know the names of three of the dozens of such people from the past few decades is really not all that informative. The fact that one of the ones from this year was apparently written about recently is similarly not informative. It is sad that he got cancer (which is exactly one of the reasons we encourage smokers to switch: to avoid getting cancer), but it is not helpful to naively look for a scientifically incorrect explanation for it.
With that, we hope you now have enough training in statistics to understand your original assessment was wrong. Humans are programmed to see causation not coincidence. It takes a bit more analysis to understand coincidence, but it is really not all that difficult.
As for your comment:
I think a survey would show most people with half a brain would agree. I think it would help your credibility not to suggest so strongly that these case are "almost certainly coincidences". Just a suggestion.
Unfortunately you are right about most people agreeing. We try to do what we can to educate a few of them enough to understand better than that. We do not think there is much to be gained by misrepresenting basic statistics just because it might help our credibility; indeed, we think it would hurt our credibility in the long run. We will stick with trying to educate.
It is impossible to determine an exact risk for oral cancer. The occurrence is so low that it cannot even be certain whether leukoplakia always precede a cancercerous or pre-cancerous lesion.
We’ve already quoted above from the Rodu & Godshall article but to add to that some indication of how daunting it is to study the intersection of smokeless tobacco and oral cancer 1. the prevalence of ST use in the U.S. is very low, about 4% among adult men and 0.3% among women (NHIS, 2000); 2. oral cancer is a rare disease, and 3. the risk of oral cancer among long-term users of ST is very low. Consider a 2005 study based on the American Cancer Society's First and Second Cancer Prevention Surveys, each enrolling over 1 million Americans in a prospective follow-up study (Cancer Causes and Control 16: 347-358). After long-term follow-up, the multivariate adjusted hazard ratios for oropharynx cancer were 2.0 (95% CI = 0.5-7.7) for CPS-I and 0.9 (CI = 0.1-6.7) for CPS-II, based on 4 cases and 1 case among ST users respectively.
It is hard to generalize about anything or be very certain of the specifics when out of over a million, you only have four or one events.