Cervical Screening – Helping You Decide

Sounds familiar, right? It’s the title of the little green information leaflet that is sent out with your invitation to attend cervical screening. Let’s look at that. It’s an invitation, and you can decide whether to take part or not. It’s a choice.

How do you make that choice? Well the leaflet has some information in it, but not all the information we need to make an informed decision, as you’ll know from previous posts on this blog. Let’s take a look at the numbers.

Organised cervical screening was introduced in the UK in 1988. Mortality rates for cervical cancer were already in decline before that. Let’s see how the screening test reduced cervical cancer deaths (source: Cancer Research UK):

Well, I suppose it went down a little bit faster, but it was already going down. Not a very dramatic change is it?

Why is that?

Cervical screening isn’t, as the leaflet agrees, a test for cancer. It is a test for abnormal cells that might, just might, become cancer. If you have abnormal cells detected with screening, you’ll likely worry, but let’s look at how likely those cells are to become cancer (invasion):

Ok, so now we can breathe a sigh of relief, well, depending on how abnormal our cells were. This is expressed as the CIN level, ranging from 1 to 3. CIN stands for cervical intraepithelial neoplasia. It’s not cancer, but sometimes these cells can change into cancer. In the table above, you can see how likely this is to happen, in the “invasion” column – this is the risk of the cells becoming cancer.

So these abnormal cells that they’re looking for don’t always become cancer. In fact, looking at the table above, it’s actually quite unusual for this to happen.

What causes these abnormal cells, which might go on to cause cervical cancer? The answer is HPV (source: https://embryo.asu.edu/pages/harald-zur-hausens-experiments-human-papillomavirus-causing-cervical-cancer-1976-1987). HPV, or human papillomavirus, is a common virus, with many subtypes.  Some cause genital warts, whereas others can cause abnormal cells, which may become cancerous. HPV subtypes 16 and 18 are the primary causes of cervical cancer. These HPV subtypes can be prevented with vaccination. HPV is sexually transmitted, from penetrative sex, and also oral sex. It is also implicated in cancers of the mouth, throat, penis and anus.

Anyway, how accurate is cervical screening?

In a previous post on this blog, we looked at sensitivity, and specificity. Let’s see what that looks like for cervical screening:

LBC stands for liquid based cytology, and is the most up-to-date method to collect smears. As we can see from this diagram, screening would wrongly tell 231 women with cancer, that they don’t have it. It would also tell 26,811 women with no disease, that they have cancer.

This is a simplified diagram, as it only takes women with actual cancer into account, not all those abnormal cells (CIN1, 2 & 3) mentioned earlier. If we factored those in, given that up to 7.7% of women might have abnormal cells at any one time (source: https://www.ncbi.nlm.nih.gov/pubmed/24305750), that’s another 7,700 women that could be given false negative, or false positive result. Even though those cells only have a small chance of becoming cancer. This could result in treatment that women don’t need.

So what does this look like?

(source: https://www.karger.com/Article/FullText/365059)

It’s a little hard to see, but when a smear test is read, and the result sent back, of the 36 women with high-grade abnormal cells, or cancer, detected, only 6 of those 36 will actually have high-grade abnormal cells, or cancer. The rest do not. Of the remaining 964 women told that they are fine, 7 of them will actually have high-grade abnormal cells, or cancer, and be told that they don’t. It’s a bit like flipping a coin for a correct diagnosis.

What about those women without abnormal cells, who are told that they have abnormal cells, or cancer, erroneously?

Let’s take a look at that:

Without screening 6 per 100,000 women will die from cervical cancer (0.006%), with screening 3 per 100,000 women will die from cervical cancer (0.003%). This is a 50% relative risk reduction, but really the actual risk reduction is 0.003% (0.006% - 0.0003%)

However, with screening, 15 women would still develop cervical cancer, and 5000 women (5%) would be diagnosed with cancer incorrectly, and treated.

So, what’s the problem with treating those 5000 women incorrectly? What’s the harm?

CIN, and cervical cancer have different treatments. Cervical cancer treatment might result in a hysterectomy, the removal of the uterus, leaving women infertile, but could well save their lives. Cervical cancer should be treated, as it can spread.

CIN treatment aims to remove the abnormal cells before they become cancer (remember the risk of this happening from above). Such treatments are LLETZ (Large loop excision of the transformation zone), Cone biopsy, Laser therapy, Cold coagulation (it’s not cold, it’s actually very hot!), and Cryotherapy (this one is actually cold). The aim of these treatments is to remove the abnormal cells from the cervix.

Whilst not everyone suffers from side effects from these treatments, there is always a risk of death from a general anaesthesia (if required) which is 1 per 100,000 patients (source:  https://www.nhs.uk/conditions/general-anaesthesia/), along with pain, bleeding and discharge.

Some treatments can cause cervical stenosis, where the cervix becomes tightly closed, prevent sperm from reaching the uterus, and fallopian tubes, causing infertility. Conversely, some treatments can cause weakening of the cervix, which is a muscle, increasing the risk of preterm birth. (Source: https://www.macmillan.org.uk/information-and-support/diagnosing/how-cancers-are-diagnosed/cervical-screening/treating-cin.html#3817)

So, should you get screened for cervical cancer? 

The answer is, it’s your choice. Being armed with all the relevant facts should allow you to make your own decision, based on your own personal situation, as to whether you wish to participate, or not.

Don’t be bullied into it by friends or doctors, make your own, informed, choice.