The Reality of Cancer Detection Tests

At a recent academic event, a guest asked about my profession. I mentioned I’m a “public hospital doctor,” which felt less intense than saying “oncologist.” His reaction, as expected, was, “Wow, isn’t that depressing?” By this point, I’ve had plenty of practice explaining that while being an oncologist can indeed feel sobering, it isn’t overwhelmingly depressing. There’s a considerable amount of good that can be done between a diagnosis and the outcome, particularly through treating the illness and offering empathy to patients.

Then he asked if there’s hope for a cancer cure. I thought of all the dedicated researchers, often underappreciated in terms of pay, and expressed that there’s plenty to celebrate in the field, along with much more to aspire to. He seemed to ponder this.

We enjoyed a pleasant conversation for the rest of the dinner, but my profession lingered in his thoughts. Before parting, he leaned closer and asked, “Can you recommend an ‘everything’ cancer test?”

I had to tell him such a test doesn’t exist, which visibly disappointed him.

That interaction came back to mind when I learned about a failed blood test that was supposed to be just what he hoped for.

The ultimate goal in cancer medicine is early detection, which could ideally lead to cures. For oncologists like myself, it would make a world of difference if we could accurately assess individual risks and catch cancer before it spreads, providing reassurance that early action can save lives.

The American company Grail (it’s a clever name, isn’t it?) introduced a blood test called Galleri designed to detect a “signal” that apparently indicates more than 50 types of cancer. This signal refers to circulating DNA, which means minute fragments of cancer DNA found in the bloodstream.

They promote the test as a screening option, emphasizing that cancer can arise at any moment. After paying nearly $1,000 for the test, a patient gets a straightforward outcome two weeks later: either a cancer signal is detected or it isn’t. Most people, about 99%, will test negative, but that 1% who tests positive will then undergo a series of further tests to determine if cancer is present.

Of course, given that this cancer test has not received FDA approval yet somehow ended up in a Super Bowl advertisement, there are quite a few disclaimers. However, one claim stood out to me: “The Galleri test aims to detect cancer signals and predict their location in the body.”

Grail then partnered with the NHS in the UK to conduct a large randomized controlled trial—the gold standard for clinical studies—to see if their blood test could lower the chances of late-stage cancer diagnoses in asymptomatic individuals.

This trial started in 2021 and involved 142,000 healthy participants aged 50 to 77. Each person provided three blood samples over two years. Half had their samples tested, while the other half received standard healthcare, which typically relies on history and physical examinations for clues.

The idea was that if the blood tests led to earlier detections, fewer individuals would face late-stage disease.

Regrettably, the trial didn’t meet its primary goal of reducing late-stage cancer diagnoses. This outcome is significant because it is the most crucial measure in clinical studies, making this failure headline news.

In response, the company announced it would expand its sales force based on “strong” results, claiming the trial “shows a notable reduction in stage 4 cancer diagnoses and improves detection in stages 1 and 2.” Despite this optimism, investors reacted negatively, resulting in nearly a 50% drop in the company’s share price and scrutiny regarding a possible class action lawsuit.

Innovative approaches to cancer research aren’t unheard of. Thanks to tireless researchers and generous patients, oncologists can now offer effective treatments that enhance life quality and longevity. Many patients I treat today would not have survived had they been diagnosed earlier in my career.

However, the fact remains: this extensive trial failed to establish a population-wide benefit for a blood test intended to catch cancer. There’s a crucial distinction between detecting additional cancers and saving lives—something that can be tough for many to grasp, but it’s essential from a public health standpoint.

For instance, detecting some cancers at stage 3 instead of stage 4 doesn’t automatically equate to less intense treatment or extended survival. Early-stage detection (stages 1 and 2) doesn’t guarantee life-saving outcomes; sometimes, these cancers might never result in harm.

This issue is particularly evident with elderly patients who, after a fall, undergo a CT scan that reveals a tiny cancer. If left undiscovered, these cancers likely wouldn’t have caused issues in their remaining lifetime, yet finding them leads to stressful interventions. While some may choose to forgo treatment, many desire action.

In certain contexts, a circulating DNA blood test could show promise, and there are researchers in Australia who are leading efforts to utilize this technology effectively.

For now, it’s crucial for healthy individuals to understand there isn’t a single blood test or “total body scan” that can definitively save lives.

This leads us back to lifestyle choices—there are practical steps we can take to lower our cancer risk. Consider reducing processed foods, curtailing alcohol consumption, quitting smoking, and engaging in regular exercise.

It might not be the kind of news that sends stock prices sky-high, but when it comes to real-world impact, the evidence is clear.