More cancer screenings sounds like good news. But can the NHS cope with them?

This month, it was reported that England’s existing screening programme for bowel cancer for 60 to 74-year-olds had prevented 20,000 cases of bowel cancer over the past 10 years. This comes amid an ongoing effort in England to extend bowel cancer screening to those aged between 50 and 59. And in June, the NHS national director for cancer welcomed a new blood test currently being trialled in the UK that can detect 50 types of the disease.

More cancer screening seems like unqualified good news: generally, the earlier cancer is diagnosed, the higher the chance of successful treatment. However, there are harms that come with screening, too, both for people being screened and for the NHS as a whole that should be mitigated against. I am certainly not discouraging people from taking up screening offers, but expansion of screening programmes must come with concrete plans about delivery. This requires extra NHS fundingand capacity.

The issue is that the large majority of people who are screened don’t have cancer. But some will nonetheless receive an ambiguous or false positive result, sending them for further testing. This is where screening can actively harm. Almost all of them will have cancer ruled out on further testing, but this can take several weeks and studies have shown that receiving a “false positive” from a cancer screening test can significantly increase anxiety and stress, lasting a few weeks to months.

This is most common in breast and prostate cancers but can also happen for others. In fact, prostate cancer screening is so unreliable that it’s not even offered by the NHS currently. Researchers must keep refining screening tests to make sure fewer people incorrectly test positive, and the NHS must make careful decisions about who should be tested and when.

Screening is also not a one-off, but is performed regularly. The chances of being wrongly sent for testing, or worse, wrongly treated, can become relatively high over the years. One recent study estimated that a 50-year-old starting bowel cancer screening today had about a 15% chance of being wrongly flagged for a colonoscopy by the time they were 74. For breast cancer, it is estimated that about 3 in every 200 women