For most of human history, a cancer diagnosis was a death sentence. Doctors could only identify cancer after it had spread extensively. Even with aggressive surgery, cancer recurred and eventually a cancer-related complication – a blood clot, infection, or organ failure – killed the patient.
Research into the mechanisms of cancer has given us options to fight back. We now have chemotherapy, radiation therapy, new surgical approaches, and so-called biological therapies, which together have dramatically increased survival rates. The strongest weapon against cancer is actually prevention: quitting smoking, reducing environmental chemical exposures, and improving diet and exercise are the best interventions against cancer.
Cancer screening is great!
But another important tool is early detection – catching cancers while they are still small and localized. For example, if you catch breast cancer while it is still localized, the survival rate is 100%! On the other hand, metastatic breast cancer – where the cancer has spread to far-away organs – has a low survival rate of about 30%.
Given this difference in survival, screening and detecting breast cancer early is essential. Medical organizations gather experts and run studies to determine when and how often to screen patients. They develop official guidelines for cancer screening that doctors then follow. For example, the U.S. Preventive Services Task Force recommends that anyone potentially at risk for breast cancer get a mammogram every two years from age 40 to 74.
Whole-body scans: not so good.
But why not take this a step further? Some longevity influencers have started campaigning to get full-body imaging to check everything from head to toe for cancer or other problems. Wellness companies now routinely offer whole-body magnetic resonance imaging (MRI), which can visualize every single organ inside you. Why don’t doctors offer this service their patients? Is there some kind of evil conspiracy in medicine to make sure people get sick?
The short answer: NO! Doctors recommend tests based on the balance between risks and benefits. When you get whole-body imaging, radiologists will always find a lot of suspicious-looking spots, which almost always end up being benign. But to confirm that they are benign, you will need to get painful and potentially dangerous biopsies or further medical testing. Sometimes a single finding leads to a cascade of test after test, which can be expensive, use up medical resources, and waste your time. Most importantly, they lead to diagnostic uncertainty: patients get stuck wondering whether they have cancer or not. This uncertainty hurts patients emotionally when they are waiting for tests to come back.
Reading the evidence
Several studies have shown exactly how much uncertainty and medical follow-up result from whole-body MRI. In a large study of 2,500 people in Germany who went through full-body MRI, about 30% had incidental findings. A panel of doctors from different specialties looked through these each of these findings together. They found that about 40% of findings were benign, 6% were potentially cancer, and the remaining 50% were unclear and required further tests or biopsies. Putting these statistics together, this is an enormous rate of follow-up testing: about 15% of participants who got full-body MRI had incidental findings that would require further testing1. A similar study in 148 volunteers in the UK found similar results: about 13% of participants had clinically-significant MRI results that required follow-up testing2.
Now, what about the benefits of early detection of cancer? If we saved many lives by detecting cancer in whole-body MRI, then perhaps we could argue that the diagnostic uncertainty is a fair trade. In a follow-up study, the group in Germany observed that participants in their study who had a finding on their whole-body MRI were twice as likely to get biopsies compared to participants who did not have any MRI findings3. This finding tells us that MRI findings did change the clinical care for participants.
The details: benefits and risks
But how much did participants benefit from the scan? We have to be careful here since people get biopsies for many reasons besides a MRI finding: maybe they noticed a lump or they had abnormal lab tests or they got an ultrasound. To account for these biopsies, the researcher broke down biopsy results two ways: 1) whether the biopsy was before the MRI study or after and 2) whether participants had an MRI finding or not. We want to answer a specific question here: if you get the MRI, what is the chance that we identify an early cancer that we would not have found if you had skipped the MRI? I’ve aggregated the data from this follow-up study with 6753 total participants below:
| Pre-study biopsies | Post-scan biopsies | No biopsy | Total | |||
| Benign | Cancer | Benign | Cancer | |||
| No MRI findings | 408 | 98 | 454 | 130 | 4641 | 5731 |
| MRI findings | 104 | 25 | 160 | 56 | 677 | 1022 |
To calculate the chance that we identify a cancer if a participant have a MRI finding, we need to focus on the post-scan columns and the MRI findings row. We find that 160+56 = 216 participants had a biopsy after the scan and 56 of them had cancer detected.
But how many of these patients got the biopsy because of the MRI finding? We can compare against the baseline (pre-study) rates. This also lets us control for the fact that people with an MRI finding may be more likely to have cancer than people without a finding. We look only at the participants who got a pre-study biopsy but would turn out to have a MRI finding after the scan. During the pre-study period, 104+25 = 129 participants got biopsies and would go on to have an MRI finding. Out of these 129, only 25 had cancer detected on the biopsy.
We can now answer our question: if you get the whole-body MRI, what is the chance that we identify an early cancer that we could not find if you had skipped the MRI? Using our dataset, we find that 56 – 25 = 31 excess participants out of the 6753 total had cancer identified after the MRI compared to before the MRI. This gives a 0.4% chance that we can catch a cancer with the MRI that we might have missed without it. Another way to put it: we’d have to scan about 200 people to catch one cancer that we might have missed.
We also need to account for the cost in terms of excess biopsies. The data tells us that we had 216 – 129 = 87 extra biopsies out of the 6753 participants, which corresponds to a 1.3% rate of excess biopsies, or about 1 excess biopsy for every 80 scans.
Correcting for time
Finally, we need to take into account that the strongest risk factor for cancer is time. Since this study occurred over a four-year time period, we know that the participants should be more likely to get biopsies and cancer after the scan compared to before the scan. To control for this factor, we can calculate the same quantities above but for participants with no MRI findings. For these participants, we expect that any change in biopsy or cancer rates are exclusively driven by time and participating in a study, rather than the whole-body MRI results.
We find 130 – 98 = 32 excess participants out of the 6753 total had cancer identified after the scan compared to before the scan, even without anything found on the scan. This is more than the excess participants in the group with MRI findings. Thus, we come to the counterintuitive conclusion that getting a scan does not catch any extra cancers!
On the other hand, we find (454 + 130) – (408 + 98) = 78 excess biopsies in this group without MRI findings. Subtracting these excess biopsies for our group with MRI findings, the corrected estimate for excess biopsies due to MRI imaging is 9 out of 6753 participants, about 0.1% or one extra biopsy for 750 scans. Thus, all that whole-body MRI scanning does is force you to get unnecessary biopsies!
Conclusions
Overall, whole-body MRI scans do not have evidence backing them. The large studies that examine the risks and benefits show a clear increase in extra biopsies without significantly increasing the chance of catching cancers early. Companies that sell whole-body scanning are only selling a false sense of security.
So why are people still going for scans? In my opinion, partly because they are marketed as a luxury commodity from the wellness industry and partly because they speak to our deep-seated fear of cancer and offer some agency. But if you do fear cancer and want to do something about it, the best things you can individually do are: stop smoking, eat better, and work out more.
Citations
- Hegenscheid, K., Seipel, R., Schmidt, C.O. et al. Potentially relevant incidental findings on research whole-body MRI in the general adult population: frequencies and management. Eur Radiol 23, 816–826 (2013). https://doi.org/10.1007/s00330-012-2636-6 ↩︎
- S.H.X. Morin, J.F.L. Cobbold, A.K.P. Lim, J. Eliahoo, E.L. Thomas, S.R. Mehta, G. Durighel, J. Fitzpatrick, J.D. Bell, S.D. Taylor-Robinson. Incidental findings in healthy control research subjects using whole-body MRI. European Journal of Radiology, 72(3), 529-533. (2009).
https://doi.org/10.1016/j.ejrad.2008.08.006. ↩︎ - Richter, A., Sierocinski, E., Singer, S. et al. The effects of incidental findings from whole-body MRI on the frequency of biopsies and detected malignancies or benign conditions in a general population cohort study. Eur J Epidemiol 35, 925–935 (2020). https://doi.org/10.1007/s10654-020-00679-4 ↩︎
All 2 Soon 