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During the height of the COVID-19 pandemic, diagnoses of some cancers in Alberta, Canada, dropped sharply, according to a new study.

In a retrospective analysis of provincial health data that included approximately 43,000 cancer diagnoses, the rate of melanoma diagnosis decreased by 43% during the state of emergency. The results suggest that the pandemic restrictions delayed cancer care among some patients.

“What was most interesting about that was that the largest drops were observed in early-stage cancers,” study author Darren Brenner, PhD, an epidemiologist and associate professor at the University of Calgary, cipro pediatrics told Medscape Medical News. The drop in early-stage diagnoses was especially pronounced for cancers targeted by organized screening programs, including colorectal and breast cancer.

The study was published online June 12 in the Canadian Medical Association Journal.

Early vs Late

The study — which revealed a significant reduction of breast cancer, prostate cancer, colorectal cancer, and melanoma diagnoses — follows reports from Ontario and other countries, including the United States and Australia, that show similar trends. Statistics Canada also recently revealed a 12% drop in new cancer cases reported to the Canadian Cancer Registry in 2020. The current research is unusual in its inclusion of data on the stage of cancer being diagnosed.

In the current analysis, researchers divided monthly data for 10 cancer types from the Alberta Cancer Registry into the following three periods: pre-COVID-19, from January 2018 to March 2020; the state of emergency period, from March to June 2020; and a 6-month period after the state of emergency (from June 2020 December 2020). Using the pre-COVID-19 data, the researchers estimated what diagnosis rates would have been had the pandemic not occurred. They acknowledge that their estimate is based on several assumptions about the data.

Rates of breast cancer, colorectal cancer, prostate cancer, and melanoma diagnoses were significantly reduced during the state of emergency, decreasing from 33% to 43%. Other cancers studied, including non-Hodgkin lymphoma and bladder, kidney, lung, cervical, and uterine cancers, were not significantly affected.

Notably, among the affected cancers, there were differences in the stage at diagnosis, suggesting that asymptomatic patients received diagnoses later than they would have with usual screening. The researchers saw a 52% drop in the diagnosis of stage I colorectal cancers, which are often asymptomatic and are detected during screenings. Similarly, there was a 53% decrease in stage I melanoma diagnosis.

Diagnosing and treating cancer early is important for improving treatment results. Each delay of 4 weeks in surgery for common cancers could result in a 6% to 8% increase in the risk of mortality, according to a meta-analysis cited in the new study.

By assessing 1-year survival, the researchers also sought to determine whether the changes in diagnoses would affect mortality. Compared with those diagnosed in 2018, patients who received a diagnosis of colorectal cancer and non-Hodgkin lymphoma during the pandemic fared worse 1 year after diagnosis. However, the impact on mortality was less robust in this short time frame, the authors acknowledge.

Brenner also noted that where diagnosis rates were not affected, there was a “good news story.” He said that this finding “speaks volumes to all of the effort that happened during that state of emergency period to ensure that life-saving procedures were prioritized.”

Screening and Catch-Up

While urgent cancer care, such as chemotherapy and surgery, remained a priority, screening programs for breast, cervical, and colorectal cancers were suspended during the 2020 state of emergency period. Of all screenings between April and June, the greatest reductions were with regard to mammograms.

“If you flip the results on their head, what it shows is that cancer screening is working in the province, it’s working in Canada. Keeping those rates high has a really notable population impact,” Brenner said.

Brenner is hopeful that efforts to catch up on screening will mitigate the effects of the disruptions in 2020. “Once we do catch up, it’s really important for people here in Alberta and elsewhere to stay up to date on their cancer screening activities,” Brenner says. “This really shows that it was working.”

“Profound Impacts”

Commenting on the results for Medscape, Linda Rabeneck, MD, MPH, of the University of Toronto, said that the study’s time frame is limited: the analysis only extends to 1-year survival rates. “Nonetheless, these are profound impacts,” she said. Rabeneck was not involved in the research.

Screening and subsequent diagnosis rates have mostly returned to their baseline values since the state of emergency ended. But some experts, such as Rabeneck, who worked on a similar study in Ontario, say that additional screenings are needed.

The decline in the diagnosis of cancers that aren’t routinely screened for (such as melanoma) likely resulted from patients’ avoidance of hospital settings and routine doctors’ visits, said Rabeneck. But the steeper decline in cancers for which patients are screened demonstrates the importance of these services.

“It’s not enough for the screening services to return to the prepandemic level, because you’ve accrued a backlog,” Rabeneck said. Especially for policymakers, she says that an essential message of the research is in regard to the importance of catching up with screening.

Without sufficient catch-up screening, the short-term disruptions caused by COVID-19 restrictions will have long-term effects through 2050, according to predictive modeling of colorectal cancer rates published in the Lancet Gastroenterology and Hepatology.

The study was supported by the Armstrong Investigatorship in Molecular Cancer Epidemiology at the Cumming School of Medicine. Brenner and Rabeneck reported no relevant financial relationships.

CMAJ. Published June 12, 2023. Full text

Gwendolyn Rak is a health reporter for Medscape and Univadis based in Brooklyn, New York.

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