Cancer

An At-home Spit Test Could Help Diagnose Prostate Cancer — And It's More Accurate Than A Blood Test

A new at-home saliva test could help identify men with a high risk of prostate cancer more accurately than blood tests, leading to earlier diagnosis and more successful treatment.

Prostate cancer is the second most common form of cancer among men, after skin cancer.

Currently, there is no standard test to screen for prostate cancer. A doctor may draw blood for a prostate-specific antigen test (PSA) or perform a rectal exam, but both of these types of screenings require follow-ups before a diagnosis can be made.

PSA blood tests measure the level of a specific molecule produced by the prostate. Yet diagnostic accuracy is compromised as an elevated PSA level can indicate a prostate issue but not necessarily prostate cancer.

The new saliva tests analyze DNA, looking for a range of small genetic changes linked to prostate cancer. Shotmedia – stock.Adobe.Com

In contrast, the new saliva tests analyze DNA, looking for a range of small genetic changes linked to prostate cancer.

Trials show this approach is more effective, and men who are categorized as high-risk because of these changes are more likely to have prostate cancer than men with elevated PSA levels.

Additionally, the spit test, which is not commercially available, falsely identified prostate cancer fewer times than the PSA test and detected a higher number of aggressive cancers that are fast-growing and more likely to spread.

"Right now, there's no reliable method to detect aggressive prostate cancer, but this study brings us a step closer to finding the disease sooner in those people who need treatment," said Naser Turabi, director of Evidence and Implementation Cancer Research UK. 

"It's encouraging to see that genetic testing might help to guide a more targeted approach to screening based on someone's risk of developing prostate cancer. More research is now needed to confirm if this tool can save lives from the disease so that it can be rolled out to improve diagnosis."

When the cancer is localized to the prostate, it is often curable. The five-year survival rate of prostate cancer, when it is detected early, is over 99%, according to the Prostate Cancer Foundation.

However, if prostate cancer spreads to other parts of the body, it can become deadly. When it metastasizes, prostate cancer commonly moves to the bones, lungs, lymph nodes, liver or brain, making early detection critical.

In the study of 6,000 European men between 55 and 69, spit samples were collected to calculate polygenic risk scores (PRSs). These PRSs were based on 130 genetic variations associated with prostate cancer.

When detected early, the five-year survival rate for prostate cancer is over 99%. Peakstock – stock.Adobe.Com

As with most types of cancer, certain groups are more at risk for prostate cancer. The average age of diagnosis is 67, and prostate cancer is considered rare in men who are under 40. African American men and Caribbean men of African ancestry are also more at risk for the disease.

Other risk factors for the disease include obesity, family history of cancer, plus factors like high blood pressure, lack of exercise and being taller than average, according to the NIH.

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In this latest study, men with the highest risk scores were referred for further screening.

Following an MRI and prostate biopsy, 40% were diagnosed with prostate cancer. Meanwhile, 78% of the men diagnosed as a result of the saliva test had a "normal" PSA level, a result that would typically indicate that no further screening is required.

Of the 187 cancers detected, 55% were aggressive cancers, compared with 36% of those identified by a PSA test in a recent study.

"With this test, it could be possible to turn the tide on prostate cancer," said Ros Eeles, a professor at the Institute of Cancer Research and a consultant at the Royal Marsden NHS Foundation Trust, which jointly led the research.

Risk factors for prostate cancer include obesity, family history of cancer, plus factors like high blood pressure, lack of exercise and being taller than average. Ratirath – stock.Adobe.Com

"We have shown that a simple, cheap spit test to identify men at higher risk due to their genetic makeup is an effective tool to catch the cancer early."

Treatment for prostate cancer includes several options, depending on the specific diagnosis. Patients may undergo surgery, chemotherapy, immunotherapy, radiation or targeted drug therapy.

In addition to the early detection and treatment of prostate cancer, researchers are hopeful the saliva test will eliminate unnecessary medical intervention in low-risk patients.

PSA tests do not differentiate between aggressive or nonaggressive tumors, leading many men to be diagnosed with cancers that would not hurt them in the long run and/or being referred for unnecessary MRI scans, invasive biopsies and other treatments.

"Building on decades of research into the genetic markers of prostate cancer, our study shows that the theory does work in practice — we can identify men at risk of aggressive cancers who need further tests and spare the men who are at lower risk from unnecessary treatments," said Eeles.

Why Rapid At-home PSA Tests For Prostate Cancer Are Fast, Convenient – And Unreliable

A recent BBC investigation questioned the accuracy of prostate-specific antigen (PSA) self-tests – rapid at-home tests for men worried about prostate cancer. The BBC analysed five of these tests using one blood sample and found varying results: one positive, three negative, and one unreadable.

PSA blood tests measures levels of PSA, a protein produced by the prostate gland. All men have some PSA in their blood but a raised level can suggest a problem with the prostate, including cancer.

In the UK, prostate cancer is the most common cancer in men. One in eight men will be diagnosed with prostate cancer during their lifetime.

Unlike many other cancers, there is no national screening programme for prostate cancer and the NHS doesn't offer routine PSA testing. But anyone who has a prostate and is over 50 years old – or over 45 and from a high-risk group – can request PSA testing on the NHS. A doctor may also request testing if they think a patient has prostate cancer symptoms or want to monitor a diagnosed prostate condition.

A faster and potentially more convenient alternative is self-testing. Currently, anyone over the age of 18 can buy a PSA self-testing kit for home use. With no proactive NHS screening programme, home testing is on the rise to catch prostate cancer early – even before there are any symptoms. By catching fast-growing cancers early, treatment can prevent them from spreading and causing serious problems.

As with COVID self-testing, the PSA home kits use test cassettes. You use a lancet (small needle) to prick your finger to get a few drops of blood, put the blood into a pipette and then drip this on to the test cassette along with a buffer solution. Depending on the test kit, a positive or negative result is displayed in five-to-ten minutes.

This might sound convenient, but some users find the detailed instructions for home PSA tests difficult to follow, which can lead to errors. A review found the information provided with self-tests is generally inadequate.

But as the BBC report showed, even when used correctly, PSA home tests can give varying results.

Not a cancer test

Positive tests or high PSA levels may cause men to worry unnecessarily. PSA tests are not blood tests for prostate cancer, and a PSA test can neither diagnose nor rule out prostate cancer. Rather, higher levels of PSA indicate a potential problem with the prostate.

In many men, this could be caused by a benign prostatic hyperplasia – an enlarged prostate. This is a non-cancerous condition affecting 8% of men in their fifties, where the prostate gland grows larger. It can cause urinary problems, such as difficulty in starting pee, a weak urine stream and frequent or urgent urination. The likelihood of developing an enlarged prostate increases with age.

An inflamed prostate (prostatitis) can also cause raised PSA, as can urine infections – and even vigorous exercise and sexual activity.

In some cases, rapid home tests can give a false negative result, offering false reassurance for users who should go on to have further tests for cancer.

Another drawback of home-testing kits is that there is no medical professional to refer a test user for further checks or to help interpret results. For example, a normal PSA level doesn't mean the person testing is cancer-free: PSA levels can be normal even in someone with prostate cancer.

Tests are not a GP substitute

While rapid at-home PSA tests can be unreliable, other types of PSA self-testing kit allow you to collect the blood sample in a small tube, then send it to a laboratory for testing. Getting these results can take a few days but can offer a more detailed PSA value, compared with rapid at-home tests. But again, these lab tests can neither diagnose nor rule out prostate cancer.

Whatever the method of testing, high PSA levels should be followed up with a doctor who can order more tests and scans to check for cancer.

Many men might find the Prostate Cancer UK online risk checker useful. It asks three main questions about age, ethnicity and family history.

The older a man is, the higher their risk of prostate cancer. Men of black ethnic heritage have double the chance of developing prostate cancer, while those with a close relative – father or brother – who has had prostate cancer are also at increased risk.

The online risk checker also provides useful resources, information to take to the doctor, and contact details for specialist nurses.

If a man is experiencing any symptoms of prostate problems, falls into a higher risk group, has genetic risk factors, has a positive PSA home-test, or just has concerns about prostate cancer, it's always best to check with the doctor – they can provide more support, information and further testing.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Dipa Kamdar does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

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