The study published by the European Association of Urology earlier this year was actually undertaken in Norwich, East Anglia, UK… who said the UK was no longer part of Europe?!
I have to say, I think this is one of the most difficult research papers I have ever had to read, let alone try and understand. The main problems are that the language is very technical, and the information is spread over the journal article as well as 4 other supplementary materials papers… why can’t people put it all in one document and use simple language that everyone can understand (at least that way no one would over or under interpret the significance of the data)?!
The research included 300 men undergoing surgery for possible prostate cancer, as well as 18 men who were being investigated for haematuria. They collected urine samples from these patients just after they underwent digital prostate examination (not digital as in computer, but digital as in finger inserted through the anus to feel the prostate through the wall of the rectum!!! Now you know where the prostate is!). Presumably they waited to collect the urine so that any bacteria in the prostate would be pushed out into the urine by the examination; they also collected the first part of the urine stream so that it was representative of prostate secretions entering the urethral urine.
Once the researchers had their urine samples, they used a number of different methods to identify bacteria including molecular assays such as 16sRNA and whole genome sequencing (which look for all of the genetic material of bacteria) and culture for anaerobic bacteria. The BBC reports “All were types of bacteria that can grow without oxygen. Some were brand new types, never found until now”. I cannot find any indication that the researchers did aerobic cultures, and they don’t say why they didn’t but if you don’t look for something rarely do you find it and this would explain why the researchers only identify anaerobic bacteria! They then identified any bacteria they found using molecular sequencing.
The researchers also tested samples of freshly removed prostate tissue, taken out during surgery, for bacteria.
Finally, they compared the identification of bacteria by 1) which stage of prostate cancer the patient had, 2) was it localised to the prostate or 3) had it spread around the body (metastasised).
So, what did they find?
The researchers found 4 completely new anaerobic bacteria in their study within the groups:
- Porphyromonas sp.*
- Varibacculum sp.
- Peptoniphilus sp.*
- Fenollaria sp.*
The researchers also showed that if you had one of the bacteria marked with a * or previously discovered Fusobacterium sp. or Anaerococcus sp. then you had a 2.6 fold higher risk of more aggressive cancer which was more likely to metastasise. That’s high and not good for the patient. So yes it’s good to identify these bugs then…
However although the researchers do say that they haven’t shown that these bacteria cause prostate cancer they do make claims that “the bacteria may influence metabolic pathways in the prostate causing cancer”. Their implication in the paper is pretty strong… that bacteria cause prostate cancer. And so, the popular press latch on to a complicated and hard to understand research paper and conclude that bacteria do cause prostate cancer!
So, what did the study do well?
The study does have some good points:
- The researchers considered the risk of contamination and tried to control it as best as possible – molecular techniques like 16sRNA and whole genome sequencing will identify ANY bacteria present, and if this is a contaminant there would be no way to tell. The researchers used meticulous handling of the specimens and used aseptic techniques to limit the risk of contaminating their samples. Added to this, if they had contaminated anything they would have contaminated all samples equally
- Reasonable case numbers (300 cases) – 300 cases is a good sample size for such a labour intensive study
- Tested tissue samples from freshly excised prostates – the researchers process samples quickly so that tissue didn’t start to “go off” which would have allowed anaerobes to become more dominant (as they do when food goes off in a kitchen!)
- Microbiological testing rigorous (culture and molecular) – the methods used to identify bacteria are cutting edge and will detect both bacteria that might grow on culture as well as those that won’t grow because they are either dead or fastidious
- The researchers do state “a limitation [of the study] is that functional links to cancer development are not yet established”
However, I do have a number of concerns about the study which the researchers haven’t addressed.
What’s not so good?
Don’t get me wrong, I do think this is a valuable study as far as it goes but I do have some reservations:
- No controls – as far as I can tell there were no real controls for this study, they took 18 samples from patients with haematuria and no concern about prostate cancer but compared to the 300 cases this does not constitute a control group. At the very least it would have been helpful to see that bacteriuria rates in completely healthy men
- No patient demographic data has been presented - the two groups of patients with and without bacteriuria could have other confounding variables that might explain the difference e.g. age, diabetes, history of recurrent UTIs, etc. Without this information it isn’t possible to say the result are just due to the presence or absence of cancer and metastases
- Culture method specifically for anaerobes – the researchers only cultured for anaerobes, as far as I can tell there was no attempt to grow aerobes which makes me think there is a predetermined bias here that anaerobes are the only bacteria that matter
- No urine sample taken pre-examination – other studies have found anaerobes in urines, and therefore they could have been present in the study population even if the prostate hadn’t been examined. This suggests another bias with the researchers believing that the bacteria were put into the urine by the prostate examination, which might not be the case
- Gentamicin was given pre prostate culture – Gentamicin does not have anaerobic activity and therefore this is a selection bias, it is likely that ONLY ANAEROBES COULD be isolated from the prostates because the Gentamicin was given before culture
- The researchers’ collected urethral urine which is very likely to contain bacteria, in fact there is a high likelihood that the urine samples would contain bacteria - (aerobic and anaerobic). Urethral urine is not usually expected to be sterile, this is another potential bias (we specifically discard urethral urine when diagnosing UTIs for this very reason and call them mid-stream urines or MSUs). How to take a urine sample - see Piddle in the bottle blog
- The researchers’ excluded patients with UTIs but they do not say how they diagnosed the UTIs – this means that we don’t know whether patients were exclude with contaminated urine samples misinterpreted as UTIs, or that there is another selection bias here with patients with normal urinary pathogens e.g. E. coli or Klebsiella spp. (that can grow aerobically) in their urine samples excluded from the study. This would mean that only anaerobes could be isolated which would “confirm” the researchers “apparent” predetermined view
- The researchers’ excluded some cultures that contained “environmental bacteria” but then gave significance to “unknown bacteria” – how do the researchers know that the environmental bacteria aren’t significant, they appear to have a predetermined view about this, another bias
- The results are inconsistent – within the data the bacteria appear to be associated with “intermediate risk” of worse cancer, but are not associated with “advanced risk” (which is considered worse still), or low risk. If the bacterial risk was consistent then the “advanced risk” should also show a difference…surely?
- Two of the new bacterial species have been named after the study's funders - Porphyromonas bobii, after the, The Bob Champion Cancer Trust and Varibaculum prostatecancerukia, after Prostate Cancer UK. Unfortunately this is unhelpful nomenclature in my opinion (although I had the pleasure of meeting Bob Champion and Aldaniti, the horse he won the Grand National on as Aldaniti was stabled just down the road from where I lived when I was a little boy).
So, what is my conclusion?
Despite the number of concerns I have about the study, and specifically the potential for bias, I do think this research raises some intriguing questions. The results certainly show patients with prostate cancer can grow bacteria from their urine and that this might be associated with an increased risk of severe disease, BUT it doesn’t confirm that the bacteria and the cancer/severity are actually related to each other. They could just both be present in older men for example.
It is this old chestnut… “I think there is more work to be done”. At the very least I think:
- The researchers in this case should go back and make sure there are no demographic differences between their patient groups,
- They should find a suitable matching control group (maybe of volunteers) to look for bacteriuria in men without prostate cancer.
- They should publish the criteria by which they diagnosed UTIs and which were therefore used to exclude people from the study.
These three things at least would remove some of my more serious misgivings about their conclusions.
At the end of the day this is a really important question. Do bacteria cause prostate cancer? If they do then it would be possible to screen urine samples for the bacteria and treat the patients with antibiotics to prevent the cancer from occurring.
Now before you say this is just science fiction I’ll remind you that we already know about at least one bacterium that causes cancer… Helicobacter pylori causes stomach cancer.
I think we have a tendency to blame the “bacteria” and reach for “antibiotics”. But as the BBC reported, Dr Sam Godfrey from Cancer Research UK says “nearly four in 10 cancers in the UK are linked to known risk factors such as smoking and obesity”, how many people are willing to reduce these KNOWN RISK FACTORS? …now where’s that urine pot? Time to send one of the 500,000 urine samples yearly that are sent to the lab …yep, wee know something about looking at wee (tee hee)!