Diagnoses of six common cancer types dropped in the early months of the coronavirus pandemic, as routine screenings were postponed by health systems and patients avoided going to the doctor for fear of contracting the virus, a new study suggests.

The study, an analysis of Quest Diagnostics data published online in the Journal of the American Medical Association Network Open, found that new diagnoses of breast, colorectal, lung, pancreatic, gastric, and esophageal cancers were down 46% between March 1 and April 18 of this year compared with the average diagnosis rates from previous years.

New findings offer grim evidence of the consequences of delayed care: A rise in undetected cancers that, when eventually diagnosed, may be more advanced and difficult to treat.

“No one is saying coronavirus prevents cancer. It just prevents getting care in a timely fashion,” said David S. Weinberg, a gastroenterologist and chair of Fox Chase Cancer Center’s department of medicine, who was not involved in the study.

At the peak of the pandemic, Pennsylvania and New Jersey were among the many states that ordered health systems to suspend all but the most urgent medical services, in an effort to preserve personal protective equipment and staff for treating a surge in COVID-19 cases, and to reduce the number of people potentially exposed to the virus. As a result, preventive screenings for cervical, colon, and breast cancer plummeted 86% to 96% in March, compared with previous years, according to a report by the medical-records company Epic.

“As much as we focused on cancer, it applies to almost everything in health care. ... To the extent we are all deferring health services, there’s a certain amount of risk that some of these conditions will advance and do more damage to our bodies than they would have otherwise,” said Harvey Kaufman, the study’s lead author and medical director at Quest Diagnostics.

Kaufman and his co-authors analyzed data from nearly 278,800 Quest Diagnostic patients between January 2018 and April 2020. They compared how often patients referred for testing had a new cancer diagnosis during a baseline period in 2018 and 2019 vs. during the early months of 2020.

The study had limitations: A disproportionate number of patients in the study group were women, and diagnosis data do not offer insight into the treatment patients received, or whether a delay in diagnosis necessarily resulted in worse health outcomes.

Still, the trend is one that worries cancer doctors.

“We have certainly been worried that cancers that could have been conceivably prevented — and there are some cancers you can pretty easily prevent — will not necessarily be intercepted at a time they can be prevented,” said Weinberg.

Routine colonoscopies, for instance, greatly reduce the risk of colon cancer. During the procedure, a scope is inserted into the colon and any polyps are removed, preventing those that may have been cancerous from developing into colon cancer.

Delayed screening could mean polyps develop into colon cancer before they are detected, Weinberg said.

Patients are beginning to return for appointments, now that doctors offices and hospitals have resumed nonurgent procedures, but many patients are still wary of exposure to the virus and have continued to delay care.

Kaufman said the latest research on delayed cancer diagnosis is an urgent reminder of why routine cancer screenings, such as colonoscopies and mammograms, are so important.

“We need health care to reach out to patients and invite them back in,” he said. “If there are opportunities to expand hours, use telemedicine to connect ... we need to think of clever ways to engage patients and bring them back.”