Wednesday, September 14, 2011


Michele Bachmann and Rick Santorum recently made some comments against vaccination in the GOP Tampa debate. I won't talk about the politics or ethics involved in their decision. But I thought it might be worth informing people about the medical science behind HPV and cervical cancer. I'll try to keep it simple without hopefully being simplistic or at least overly simplistic. Physicians and scientists may take issue with what I've said or how I've said it, but I hope they'll keep in mind I'm attempting to target the average person. But if any of the information is incorrect, I'd appreciate and welcome correction so that this post gives people accurate information.

Human papillomavirus (HPV) is a virus. Like many other viruses, HPV is essentially DNA surrounded by a protective coat (as seen in the above image). HPV can infect areas of our bodies lined with what's called mucus membrane (among other places). This includes a woman's cervix since it's lined with mucus membrane. HPV can infect the cervix and over time damage the cervix. HPV is an oncovirus or virus which can cause cancer. As such, it's the most important risk factor in the development of cervical cancer.

The development of cervical cancer from HPV infection begins when HPV damages the cervical cells in such a way as to begin to change their structure and function. This leads the normal cervix to undergo what's called cervical intraepithelial neoplasia (CIN). CIN is a precursor to cervical cancer. CIN can lead to cervical cancer.

CIN progresses in three stages: CIN I, II, and III.

Here's a slide of a normal cervix taken from a special type of microscope looking at a relevant portion of the cervix:

Here's a slide of the same but in CIN I:

Here's a slide of the same but in CIN II:

Here's a slide of the same but in CIN III:

Note the progressively worsening changes in the above slides. Each of these slides contains a bunch of cervical cells. Note how the cells change in their size and shape. Also, note how the cells begin to look less and less different or differentiated from one another and more and more like one another. Further note how these cells are proliferating. And likewise note how far down the cells have begun to invade.

Or let's take a closer look. Let's zoom in and look at the cells themselves.

Here are some normal cervical cells:




Although stains have their purposes, we can more or less ignore the stains or colors for our purposes. What's important is that each of these are cervical cells and that they have a nucleus. Thus, in addition to what we noted above, note also the change in the ratio of the nucleus to the cytoplasm (the stuff around the nucleus but still inside the cell). The nucleus begins to take up more and more of the cell.

Now, CIN III is carcinoma in situ or stage 0 of cervical cancer. After CIN III, we'd have cervical cancer stages I to IV.

Anyway, hopefully people have understood everything thus far. If so, then one can understand that these aforementioned changes are signs which point toward the development of cancer.

However, it's not necessarily the case that HPV will definitely cause cervical cancer. Rather, only a very small number of HPV infections will eventually result in cervical cancer. And the most common type of cervical cancer is squamous cell carcinoma.

At the same time, vaccination doesn't necessarily guarantee cervical cancer will never develop. There are well over 100 different types of HPVs. We don't have vaccines against all of them. But the most commonly used HPV vaccine (Gardasil) has been shown to protect against approximately 70% of HPVs which do cause HPV.

In the US, cervical cancer is the 8th most common cancer for women. Although I believe it used to be the 5th most common cancer for women without HPV screening (pap smears) and vaccination programs in place. In 2007, 11,150 women were diagnosed with cervical cancer and 3,670 women died as a result of cervical cancer.

However, HPV prevalence does vary with the age of the woman:

What's more, HPV can cause other diseases including other types of cancer (e.g. penile), CIN as we already mentioned, genital warts, etc. So it's not solely cervical cancer that's possible with HPV infection.

Of course, if more people were abstinent until marriage and monogamous, all this would probably be a much smaller problem. But that's unlikely to happen in our society and culture.

I'd like to note much of the information and many of images were taken from a classic pathology textbook, Robbins and Cotran Pathological Basis of Disease (8th ed.). If my post was too simple for some or if some would like more information, then I'd highly recommend reading the section on cervical cancer in Robbins for detailed and better presented information. Of course, pathologists would know of even better resources.

No comments:

Post a Comment