HPV Throat Cancer - Running the numbers

[Freaker]

Docs,

I realize I am obsessing about this issue but that realization does not help me stop obsessing! I have an appointment with a shrink on Monday to talk about this. But in the meantime, it helps me to relax about this to try to actually quantify the risk. And so, the following post:

With respect to this issue, you have stated that given the prevalence of HPV-16 and oral sex, the fact that only 10,000 cases of HPV-related cancer occurs per year is evidence that it is very unlikely that one would develop cancer from an act of performing oral.

I wanted to try to quantify this, as follows.

If it takes, say, 20 years between contracting oral HPV-16, and the devolpment of cancer, I looked at the US population in 1990 - which was roughly 250,000,000. Of this figure, I estimated that there would be about 75,000,000 women who are a sexually active age. Assuming that prevalence of HPV-16 in the female population was about the same as it is now (1.5% according to this study - http://jama.ama-assn.org/content/297/8/813.full) that would mean there were about 1.1 million women with HPV at that time.

Assuming that, conservatively, 1 out 3 of those women had oral sex performed on them by a man in one year, that would mean that there were 330,000 men orally exposed to HPV-16 in 1990.

Now, 20 years later, about 6,000 men a year are diagnosed with HPV-related throat cancer. That would mean roughly 1.8% of men (6,000 out of 330,000) who performed oral sex on a woman with genital HPV developed HPV-related throat cancer.

I know that, obviously, there are a lot of assumptions built into this calculation - but would you more or less agree with the conclusions, or am I missing some major factor? I know there could be other circumstances like whether someone was also a smoker etc., but a lot of studies have said that HPV is a separate unrelated risk factor (Such as this one: http://www.ncbi.nlm.nih.gov/pubmed/18334711).

Thanks

[Edward W Hook, MD]

It's complied data, mostly form studies done at University of Washington

EWH

[Freaker]

Thanks for your time. If you could tell me where you get the statistic that about 50% of people get HPV-16, I think I can forget about this issue.

I would appreciate it.

[Edward W Hook, MD]

I don't mean to sound uncaring but calculations  on the topic of throat cancer following oral sex using imprecise numbers has less basis in fact than calculation your chance of getting struck by lightning. Part of the reason for this is that we have far better information on how lightening is formed and how often it occurs than we do for oral HPV or for cancer of the throat.  The information on this topic is emerging however, if this were a common event we would have an epidemic of oral cancer and we do not.

Current estimates at the about 70-75% of American adults have participated in oral sex and for most people this is not a single, isolated event.  As I also said, most Americans will get HPV and about half will get HPV 16.  Finally the biological interactions between co-factors is likely multiplicative in terms of amplification of risk, not additive.  

Finally, in answer to your question, I tried to simplify things, perhaps a bit too much.  At least in the genital track (again, not much is known about oral infection), All HPVs are not equal in their average duration of infection, with types 16 and 18 persisting, on average, somewhat longer than many other types.  For this reason, as I said before, your estimates of exposure are underestimates.  All of this variation contributes to imprecision in the mathematical exercise you are engaging in.  On this forum when "reasoning" based on terribly imprecise assumptions leads to conclusions that cannot be substantiated by scientific study (at least as yet), we choose not to participate. That is the case here.  I'll have nothing more to say other than, for now, there is no reasons to engage in major worry about the risk of cancer of the throat following oral sex.  If it worries you that much- don't do it.  If you've already done with it, live with it.  

Take care. EWH

[zebbe]

one thing for oral cancer and HPV affects both men and women, the risk of infection and the presence of HPV in the throat has been shown to be the same, and I am quite convinced that giving oral sex is more common in women than men, in this perspective should both HPV infection and cancer is more common in women, but reality says that only 33% of women remaining men who suffer from cancer, yet another factor that suggests other factors are more common in men as alcohol, smoking, poor diet and hygiene

[zebbe]

but I understand what you mean by the number of men, 6000 in 20 years will be 120,000 men, but then you must also count how many times men have been exposed to infection in these years.
tll example, 330 000 52 times in a year for 20 years it become 343.200000, 120000 / gives 0035%

[zebbe]

If you are going to use all women who have ever had HPV-16 wouldnt you then have to calculate based on all the men that have ever had HPV related throat cancer - and not just the 6000 that get it a year? So wouldnt the numbers end up being the same?


You think wrong, though many more women are infected you will also be many more men infected, it is reasonable, but then drops course the statistics of how much risk there is HPV in the mouth cause cancer, the more people who have the means to the percentage that ends with cancer is even less

[zebbe]

you make a small calculation errors beyond what the doctor writes and that is that you count the number of infections as an opportunity to get infected, you have to count the number of infection cases that is how often an infected person has oral sex, as you count it once a year , which is unlikely, expect instead of oral sex maybe once a week, then you will get once your number by 52! This means that oral cancer may be linked to oral sex, but oral sex is not associated with oral cancer, this is a big difference, I have an interesting report on HPV and smoking, email me if d want me to send it. for you must remember that these 6000 cases, it is less than 20% are non-smokers

[Freaker]

Doc - Just one brief follow up which I think is not much to ask for 20 bucks -

If you are going to use all women who have ever had HPV-16 wouldnt you then have to calculate based on all the men that have ever had HPV related throat cancer - and not just the 6000 that get it a year? So wouldnt the numbers end up being the same?

[Edward W Hook, MD]

I won't get into a "what if" discussion here however, I disagree with the basis of your calculations. Specifically, that the prevalence of HPV 16 is/was 1.5%.  The proper denominator for such calculations is the number of women who have ever had HPV, not the number who have HPV at any instant in time since that is the number who could potential transmit infection at any time.  Thus, the denominator is about 25-30 times higher than your estimate as at least 40-50% or women will have HPV 16 at some point.

Further, you misunderstand the statistical methods used in some of your sources.  While HPV is an independent risk factor for cancer, that risk is not unrelated and the other factors such as smoking interact with the HPV to amplify risk.  

I’ll have nothing more to say about this.  I’m pleased for you that you will be seeing a mental health professional to move past your concerns.   Take care.  EWH