Cancer is a reality that many of us will have to confront in our lives, either personally or with our loved ones. It affects one in two people at some point during their lifetime. Early detection and prompt treatment are crucial in improving outcomes for cancer patients. This is why the recent development of a new test by the NHS has generated so much excitement. The test has the potential to revolutionize cancer care by detecting the presence of 50 different types of cancer through a single blood sample, even in individuals who do not exhibit any obvious symptoms. It was announced in June that this test could be made available to a million people as early as next summer. The implications of this breakthrough are significant.
However, upon closer examination of the evidence, it becomes apparent that the reality is not as straightforward as the initial hype suggests. While this test may be an improvement compared to some existing cancer tests, it cannot currently serve as a standalone diagnostic tool. Relying solely on this test could lead to problems, especially if the individual does not actually have cancer. In essence, it is a “tale of two tests,” as Charles Dickens would say.
To illustrate this point, let’s consider two patient scenarios. The first patient experienced severe back pain after a minor fall and sought medical attention in A&E. A scan revealed that she had cancer in her bones, which had spread from an undiagnosed breast cancer. Interestingly, a few years prior, she had noticed a lump and skin tethering, and she also had a family history of breast cancer. Despite these indicators, she assumed that her routine mammogram appointment would provide the necessary answers. Unfortunately, the scan results came back as normal, leading her to celebrate erroneously. It was only a couple of years later, after experiencing weight loss, fatigue, and another fall, that she received a correct diagnosis of cancer in A&E. This case highlights the importance of considering the patient’s symptoms and risk factors in conjunction with test results. Even if the initial scan is normal, further examination may still be necessary.
In contrast, the second patient, an American businessman in his 40s, underwent a routine medical checkup that included a prostate-specific antigen (PSA) test for prostate cancer. Despite being healthy and showing no symptoms, his PSA test results came back as positive, leading to unnecessary biopsies. Thankfully, the results proved negative for cancer. However, he subsequently experienced complications such as erectile dysfunction. His pain and urinary difficulties ultimately required medical attention, and it was discovered that they resulted from an infection caused by the biopsies. This case demonstrates the potential risks of false-positive test results and the subsequent cascade of unnecessary interventions and complications.
These two stories expose the shortcomings of current cancer testing methods and shed light on why the newly celebrated Galleri test might not live up to its hype. In a recent study led by Oxford University, over 5,000 individuals in England and Wales who were referred to the hospital with suspected cancer were given the Galleri test alongside other routine diagnostic tests. The results, presented at the American Society of Oncology annual conference, showed that the Galleri test accurately identified two-thirds of cancers. News outlets reported that this test had the potential to detect and rule out cancer in individuals with symptoms, which could be a transformative development. However, this interpretation is misleading because the Galleri test cannot definitively rule out cancer in symptomatic individuals.
The original studies on the Galleri test, published in the Annals of Oncology in 2021, revealed that its specificity, or ability to accurately identify individuals without cancer, was an impressive 99.5%. However, its sensitivity, or ability to detect cases of cancer, was only 51.5%. This means that slightly over half of individuals with cancer would test positive, while the rest would go undetected. For individuals with early-stage cancer, the test’s ability to detect cancer dropped to just 16.8%. Therefore, it is entirely possible that the Galleri test could have missed the breast cancer in the first patient mentioned earlier. Consequently, relying solely on the Galleri test to rule out cancer for individuals with symptoms, such as the presence of blood in their stool, is not advisable. Additional tests, including colonoscopies, should still be performed.
However, where the Galleri test could prove valuable is in cancer screening programs. The NHS is currently conducting a trial involving more than 140,000 individuals to determine whether this blood test enhances early cancer detection. With its 99.5% specificity, the Galleri test has the potential to spare individuals unnecessary interventions and complications like those experienced by the American patient who underwent the less accurate PSA test. Therefore, the Galleri test could play a role in saving lives by identifying asymptomatic individuals who would otherwise go undiagnosed.
Nevertheless, it is crucial to consider the cost implications of implementing such a test on a national scale. The Galleri test is estimated to cost around $900 in the U.S., and when extrapolated to a large population, the financial burden would be substantial for identifying only a few additional cancer cases. Moreover, false-positive test results necessitate further investigations, which can potentially harm individuals.
In conclusion, while the Galleri test shows promise in enhancing cancer screening and detection, it is not a foolproof solution. Its limitations, including lower sensitivity and potential false-positive results, must be recognized. Leveraging this test in conjunction with other diagnostic methods is crucial for accurate cancer diagnosis. Additionally, cost-effectiveness and potential harms must be carefully considered before widespread implementation. As healthcare professionals, we must remain cautious and critical in our assessment of new tests and technologies, ensuring that patient safety remains the top priority.
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