A medical radiology manipulator adjusts the position of a patient's arms for a lung scan — first opinion coverage from STAT
A health care worker prepares a patient for a lung scan.PASCAL POCHARD-CASABIANCA/AFP via Getty Images

When the U.S. health care system pivoted to meet Covid-19 in 2020, routine health visits and screenings where many cancer cases would have been caught didn’t happen. It wasn’t ideal, but many health experts thought that as the country opened back up, screenings would help “catch up” to these missed cases. A new paper published Monday in JAMA Network Open suggests that didn’t happen as quickly as experts had hoped.

Instead, the new analysis suggests that cancer diagnoses recovered to pre-pandemic levels by the end of 2021 — but didn’t make up for any of the lost cases from earlier in the pandemic. That leaves a troubling mystery for epidemiologists, as it means experts still don’t know what happened with the roughly 130,000 cancer cases that were missed in 2020.

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“It’s still an unwritten story as to what exactly is going on,” said Uriel Kim, a population health scientist at Case Western Reserve University and the lead author on the study.

Patients can get diagnosed with cancer in a few ways. The first is through recommended screenings like mammograms, colonoscopies, pap smears, and chest CTs for lung cancer. Other ways include regular visits with primary care physicians who may recognize certain symptoms or complaints as signs of cancer, catastrophic symptoms that reflect an underlying cancer, or findings or imaging for other problems that incidentally reveal an undiagnosed tumor.

The pandemic disrupted a lot of that, as Covid-19 shifted both patients’ and health professionals’ priorities, and cancer experts widely expected there would be a big drop in cancer diagnoses. “The second year, what happened in 2021, is more important long-term, because it tells us where we did not make up,” said Todd Burus, a data scientist and Ph.D. student at the University of Kentucky who did not work on the study.  

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To do the study, scientists created a mathematical model that projected how many cancer diagnoses were expected in a given year. Then, they compared those figures against the number of observed cancer diagnoses for the year from the National Cancer Institute’s SEER database. Kim and his colleagues saw a very distinct gap between the expected cases and observed cases in 2020, but the study showed diagnoses recovered to roughly pre-pandemic levels in 2021.

“We were very close to the project incidence” for 2021, Kim said. “But not enough to cover the deficit we had in 2020.”

The gap of roughly 130,000 cases in 2020 aligns with other analyses done in the last year, including work from Kentucky’s Burus. However, in a study he led in September, Burus found that a deficit in cancer cases remained in 2021 — suggesting that Covid had continued to hamper the regular discovery of cancer cases in the second year of the pandemic.

At the moment, there’s just not enough data to understand what’s happened to the tens of thousands of missing cancer cases, experts said. The best-case scenario is that many of these cases were caught in later years — 2022 and after — without cancers advancing to later stages.  

Worse-case scenarios include the possibility that some of the people who would have been diagnosed with cancer by now have already died of other causes — potentially due to Covid-19 infection. In both Burus’ and Kim’s analyses, lung cancer diagnoses, in particular, remained lower than expected in 2021, and patients predisposed to that disease may have also been more vulnerable to Covid-19.

“Smokers, maybe people with respiratory issues — the overlap from potential deaths from Covid and cancer would be greatest for people predisposed to lung cancer,” said Siran Koroukian, a population health scientist at Case Western and senior author on the study. Still more people may have died from an undiagnosed cancer that wasn’t included in national cancer databases from autopsy reports.

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But by far the biggest concern is that many of the people who would have been caught with early-stage cancers will show up with later-stage cancers. “I don’t know that we’ve seen strong evidence of an excess of late stage yet,” said Kentucky’s Burus. Though, that may still show up later on — as data from later years become available to scientists to analyze.  

For now, health scientists will simply have to wait for those data to arrive. Burus said it will likely be years from now before it’s clear what happened to everyone who went undiagnosed in 2020. “That’s unfortunate, and not helpful for those individuals, unfortunately,” he said.

But monitoring the data and watching for where those cases show up might help the health care system adapt better to future challenges, Burus said. Doing so, he added, could also help experts better understand how to catch patients who would otherwise slip through the cracks.