PROFESSOR ROB GALLOWAY: With plans to roll it out to a million people next year… That’s why I wouldn’t want to rely on the new NHS blood test to see if I had cancer

Cancer is something many of us – or our loved ones – will face at some point, affecting one in two people in their lifetime. Getting an early diagnosis and starting treatment is key.

That’s why there’s been so much excitement about a new test currently being trialled by the NHS, both for people with cancer symptoms and those who have no obvious signs of it.

And in June it was announced that this new test can be offered to a million people from next summer.

The suggestion is that it “could transform cancer care.”

The test in question, in case you missed all the headlines, is the Galleri test: It looks for DNA markers from 50 types of cancer in a single blood sample.

However, as I’ve found out by taking a closer look at the evidence, it’s not as simple as the hype surrounding it would lead you to believe.

And while it may be better than some current cancer tests, you wouldn’t want to rely on it as a standalone diagnosis at this stage — and it could cause real problems if you don’t actually have the disease.

To paraphrase Charles Dickens, it’s a “story of two tests.”

Let me explain. Take the patient I saw who came to the ER with severe pain in her back after a minor fall. A scan showed she had cancer in her bones, which had spread from a previously undiagnosed breast cancer.

A few years earlier, she had noticed a lump and skin adhesion. She also had a family history of breast cancer.

She was terrified and also afraid of hospitals and doctors. But as she already had a routine appointment for a mammogram (as part of the NHS screening programme) she thought ‘this will tell me the answer anyway’. And when the scan results came back to normal, she celebrated.

But a few years later, she lost weight, felt tired, and fell, which led to her diagnosis in the emergency room.

The original mammogram had been reviewed by an expert breast radiologist, but they had no knowledge of her symptoms and risks and would simply have thought it was a routine screening test.

Did this matter? In fact, context matters when judging test results: The fact that she had symptoms and a family history meant she had to be seen in a breast cancer clinic, even if the scan didn’t pick up the cancer.

This is very different from one of my other patients, an American who was on a business trip in the UK when he started having severe pain and was unable to urinate. Cause? An unnecessary check for prostate cancer.

A healthy man in his 40s, with no symptoms, his job as a banker meant he had annual medicals, including a PSA (prostate-specific antigen) test for prostate cancer.

It came back positive and he had two biopsies. But although his results thankfully turned out to be negative, he started having problems getting an erection – very important, especially since he had started a new relationship.

Shortly before arriving in England, he started having painful urination, but during a meeting the pain got worse and he was rushed to the ER. His symptoms were caused by an infection from the biopsies and he required antibiotics and a catheter to help him urinate.

These two stories highlight the flaws in cancer testing, and why the new “miracle” test may not be all it’s cracked up to be.

In the first case, the patient was told she had a negative test when in fact she had cancer (‘false negative’).

In the second case, the PSA test came back positive when in fact he had no cancer – a “false positive.”

The best tests have as few of these misdiagnoses as possible, and as techniques improve, error rates will decrease.

But no test will ever be 100 percent perfect. We use the term “sensitivity” as a measure of the likelihood of a test missing a cancer diagnosis if you actually have cancer.

So if a particular test is 100 percent sensitive, you can be 100 percent sure you don’t have cancer if the test is negative. Unfortunately, while mammograms are quite good, they are not 100 percent sensitive, but 85 percent. So if your result is negative for cancer, there is still a small chance that you have the disease. This is the scenario that many of us would find most concerning.

Another measure, ‘specificity’, is the chance of testing negative if you don’t have the condition – in an ideal world a test would be 100 percent specific: so if you then tested positive, it would mean you definitely have cancer . Unfortunately, for my US patient, the PSA test is not 100 percent specific; it’s more like 80-90 percent, which meant “cancer” was misdiagnosed and he had unnecessary biopsies and subsequent complications. And all this is why we should be less enthusiastic about the Galleri test.

In a study led by the University of Oxford, 5,461 people in England and Wales who had been referred to hospital by their GP with suspected cancer were given the Galleri test, as well as the other routine test they would normally be given, such as a colonoscopy for suspected bowel cancer . cancer

The results, presented at the annual conference of the American Society of Oncology in May, showed that the test correctly identified two-thirds of cancers.

The Guardian newspaper reported that this test “has the potential to detect and rule out cancer in people with symptoms” – imagine how transformative this would be. But this suggestion was based on a worrying misunderstanding, because the Galleri test emphatically cannot “rule out” cancer in people with symptoms.

The original studies on the Galleri test, published in 2021 in the Annals of Oncology, showed that the specificity was 99.5 percent — in other words, 99.5 percent of people without cancer tested negative — which is very impressive.

But the sensitivity was only 51.5 percent, that is, just over half of the people with cancer tested positive – the other half missed completely.

And the number of people who tested positive was much lower (16.8 percent) if they had early stage cancer – before it has spread and when it is easier to cure.

So the Galleri could have missed my breast cancer patient and I wouldn’t want to use this test, for example, to rule out cancer in a patient with symptoms such as blood in the stool without other further tests, including a colonoscopy.

But where it could be useful is in screening. The NHS is conducting a trial of more than 140,000 people to see if using this blood test helps detect more cancers at an early stage. The 99.5 percent specificity means that if my American patient had it, he might have been spared the biopsy and infection that the less accurate PSA test led to.

Used alone without any other test, the Galleri would miss true cancers — about 84 percent of those in the early stages of cancer and about half of all cancers overall. So it can never be used as the only test for cancer for people with symptoms.

However, where it can be useful in screening is picking up some patients with no symptoms who would otherwise not receive a diagnosis at all. These people could save their lives.

But at what price? The test costs about $900 (about £700) in the US and on a national scale that would mean a lot of money to detect a few extra cases of cancer.

And it’s not just the financial cost, there are those other people who will be harmed by the false positive test results that need further investigation.

We should also be aware that some people with cancer who test negative assume they don’t have cancer and ignore their symptoms, when without the test they would have sought medical help sooner.

If I had symptoms of cancer, I would consider requesting the test as an additional measure to help the doctors.

But if I were in charge of the NHS budget I would need a lot more convincing that this was the best way to spend vital resources to reduce cancer deaths.

• Twitter: @DrRobgalloway

What’s in a name?

This week: Tailor’s buttocks

Pain in the buttocks after prolonged sitting is medically known as ischiogluteal bursitis – but because it “traditionally affects people who sit on hard surfaces for hours on end, the more common name is weaver’s or tailor’s buttocks,” explains Sampada Bhide, advanced physiotherapist at Kingston Hospital NHS Foundation Trust, Surrey.

Sitting in the same position for long periods of time can put pressure on the bursae (the fluid-filled sacs that act as a cushion between the muscles and the sit bones), causing inflammation and pain.

It is more common in older, weaker people and is also seen in cyclists who use hard saddles. Anti-inflammatories and a well-placed pillow can help, says Sampada, as can sit-to-stand squats with a chair or bridges (where you lie on your back with your knees bent before lifting your hips off the floor, keeping them in line with your knees and hold them for a few seconds before relaxing).