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Re-inventing the finger

In the first of five articles short-listed for the ICR's Mel Greaves Science Writing Prize 2015, the winner Dr Hugh Harvey writes about re-inventing an age-old test for prostate cancer.

My father, who recently retired at the age of 65, rang me the other day to ask me for some personal medical advice. Being the only medically trained family member I’m used to being a free source of clinical knowledge, from warts to minor surgery, but we’ve always shied away from discussing the really intimate, embarrassing, icky medical things. That was, until now.

“Should I get my prostate checked?” he asked, quite matter of fact. “A chap at golf just found out he’s got a bit of prostate cancer, so… it got me thinking...”

A short pause followed while I tried to delete the mental image of my father’s behind being subjected to a surgeon’s finger. However, I can understand why he’s asked me – not only does he fit the required demographics of age and sex for the disease, but I also happen to be doing a ‘fancy research degree’ in the imaging of prostate cancer.

“I’d speak to your GP about it,” I replied. “They have some decent tests for this sort of thing.” I semi-lied, semi-dodged. The truth, as always, is slightly more complicated than that. The current tests we have for early prostate cancer are actually embarrassingly inaccurate.

Since time immemorial the physical exam has been a cornerstone of medical practice. Doctors have been poking and prodding their way through patients since before Hippocrates oathed his way into the mainstream. It’s only through an obtuse quirk of anatomical fate that doctors can even manage to examine the prostate at all: the adult human index finger just so happens to be long enough to reach the position of the prostate, which just so happens to lie right next to the back passage. (Creationists would say God made it that way, evolutionists may suggest our fingers evolved in order to reach the prostate – I’m not sure either is correct.)

What are doctors feeling for anyway? We have known for some time that prostate cancer tissue is stiffer than normal prostate tissue, and this is due to an increased cellular density as cancer cells proliferate. Doctors can feel this difference in stiffness with their fingertip (the tip of your finger contains the densest area of nerve receptors anywhere in the entire body). They will prod and push against the prostate, testing how firm it is, and then, judging from their experience, they make a subjective assessment of how much cancer they think there is within the gland. This test has a dubiously variable accuracy rate depending on which doctor you ask, how experienced they are, or what they had for breakfast. In fact one 2012 study proved that it was next to impossible for a doctor to feel the entire prostate anyway! So what’s the point?

Unfortunately our diagnostic arsenal is otherwise limited. The other first-line tests at our disposal include a blood test for prostate-specific antigen (PSA), which is known to be hugely unreliable. Even Dr Richard Ablin, the man who invented the test, called its widespread use a “hugely expensive public health disaster” in an article he wrote for the New York Times. Add to this the less than 50% chance of actually finding a cancer on ultrasound-guided biopsy (the current standard biopsy procedure takes 10–12 samples at random sites from the prostate), and you can see just how blind we really are. It sometimes seems a miracle that we find prostate cancer at all! (This is why there is no national screening programme for prostate cancer, of the ilk equivalent to breast cancer in women.)

These days a combination of age, abnormal finger test, high PSA and luck will get men seen by a specialist, who will often refer them on for an MRI of the prostate. This high-tech form of imaging not only details the exact anatomy of the gland, but also uses relatively new imaging techniques to assess how different parts are functioning. The denser, stiffer cancerous tissue can light up on special sequences designed to look for restricted water movement, and new cancer-related blood vessels are visible when contrast dye is injected. MRI has revolutionised the detection process, and undoubtedly become the preferred diagnostic test for both patients and doctors. It not only finds cancer, it informs where to biopsy in order to confirm cancer. The only problem is – it’s far too expensive to justify using it as a national screening tool. One scan can cost between £400–800 depending on how fancy a machine you use (and how much the radiologist charges).

There is a new technology, however, which shows some promise in filling the void between the next-to-useless finger examination and eye-wateringly expensive MRI scans. Using very low frequency sound waves, prostate tissue can be ‘vibrated’ and an ultrasound receiver can listen for the echoes of these vibrations, or shear waves as they are known. Since 1991, when Dr Ophir discovered that you can use this to measure the stiffness of tissues, physicists have been working on applications in the medical world. For instance, there has been success in assessing liver stiffness in alcoholics and people with liver disease with a device called FibroscanTM .

Shear wave elastography (SWE) has been incorporated into a small ultrasound probe roughly the same size as a doctor’s finger that fits inside the back passage. This probe is then pointed at different parts of the prostate. Shear waves are sent out from and then received by the same probe, and a stiffness value is calculated – just like a digitised version of a doctor’s finger, but more reliable. As part of the PROFILE trial at the ICR, this technology will be compared with MRI scans in the same men. If the results come back with enough accuracy (i.e. we can confidently say when someone doesn’t have cancer) then SWE could ultimately be considered as a screening tool.

In other words, it may turn out that when it comes to prostate cancer screening we didn’t need to re-invent the wheel – just the finger.

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