A new study based on data collected from Alberta, Canada, shows significant drops in the diagnoses of breast, colorectal, and prostate cancers as well as melanoma, likely due to the delay of routine screenings and cancellations of health care visits during the first part of the pandemic.
The study is published in CMAJ (Canadian Medical Association Journal).
The research team measured survival rates for three groups of patients diagnosed between January 2018 and March 2019, March 2019 to March 2020, and March of 2020 through December 2020. The post-pandemic group was divided further into a "state of emergency" (SOE) phase (March 16 to June 15, 2020) and post-SOE phase (June 16 to December 15, 2020).
The authors write the first wave of COVID-19 reached its peak in Alberta on April 30, 2020, and active cases started to decrease. By mid June, the government lifted some restrictions on medical clinic shutdowns.
Breast diagnoses dropped by more than one-third after March 2020
In total, 42,862 cancer diagnoses were included in the analysis.
During the SOE period, researchers noted significant drops in diagnosis rates of melanoma (43%), colorectal and prostate cancer (36%), and breast cancer (33%). After the SOE lifted, the monthly diagnoses recovered at a 10% rate per month (incidence rate ratio [IRR] 1.10, 95% confidence interval [CI] 1.06 to 1.13).
The authors then built a counterfactual model to determine diagnoses if the SOE had not occurred. They found an additional 350 breast cancers, 398 colorectal cancers, 484 prostate cancers, and 223 melanomas would have been diagnosed between March and December 2020.
By December of 2020, the incident rates returned to pre-pandemic levels, the authors said.
"According to our model, 1455 diagnoses of these 4 cancers could have been missed in 2020. The decrease in diagnoses during the state of emergency was more evident in early-stage cancers (especially stage I) than stage IV cancers," the authors said. "Unstaged melanoma, colorectal and prostate cancers also showed a significant decrease."
The sweeping and unprecedented measures enacted at the beginning of the COVID-19 pandemic in Alberta had an inevitable impact on cancer care.
The findings corroborate trends seen in others part of Canada, the authors said. In Ontario, there was a 34% drop in new cancer diagnoses in April 2020, and Manitoba had a 23% reduction in the same period.
"The sweeping and unprecedented measures enacted at the beginning of the COVID-19 pandemic in Alberta had an inevitable impact on cancer care," said Darren Brenner, PhD, an associate professor at the University of Calgary's Cumming School of Medicine, in a press release on the study. "Even though treatment and urgent surgeries for cancers were prioritized when other procedures were delayed or cancelled, preventive and diagnostic services were greatly reduced."
