COVID-19 Has Created a Backlog of Undiagnosed Cancers, Including Melanoma


By Erin Bekes

In a study by Dr. Antoine Eskander and colleagues described in the Journal of the National Comprehensive Cancer Network, Canadian researchers studied how the COVID-19 pandemic affected the number of cancers diagnosed each week in the province of Ontario. They found that fewer patients were diagnosed with cancer during the first six and one-half months of the COVID-19 pandemic compared with before the pandemic. The biggest drops were seen for melanoma, cervical, endocrine, and prostate cancers: less than half the expected numbers of these cancers were detected weekly after the start of the COVID-19 pandemic. Recovery in cancer detection was slow, and as of September 2020, the number of new cancers diagnosed each week had not caught up to the pre-pandemic level.

The researchers estimate that there is a large backlog of cancers—including melanoma—that have gone undetected because of healthcare disruptions during the COVID-19 pandemic.

Why is early detection so important?

Detecting cancer early increases survival. Melanoma caught early, before it has spread to other parts of the body, has a much better prognosis and is generally treatable with surgery. Some cancers can be detected early through preventative screening programs – for example, women are routinely screened for cervical cancer, and melanoma can be detected through annual skin check appointments or other checkups. However, for cancer to be detected early, people must attend the necessary screenings and appointments and address new symptoms and medical concerns at those healthcare appointments. With doctors’ offices closed and patients reluctant to go back to appointments, the COVID-19 pandemic disrupted access to healthcare for routine medical issues, including cancer screenings.

How was this study set up?

Earlier studies suggest that fewer people were diagnosed with cancer at the beginning of the COVID-19 pandemic, but this question has been difficult to study over time. The difficulty is that many countries do not have an organized system to collect information about all of the cancer cases that occur in the people who live there. In Ontario, Canada, information about each patient who is diagnosed with cancer or who died due to cancer is entered into a centralized database, called the Ontario Cancer Registry, within one month. Because this database includes such complete information (>95% of cancers are included), the researchers used this database to assess the impact of the COVID-19 pandemic on new cancer diagnoses in Ontario.

Information about all of the 358,487 adults who were diagnosed with cancer in Ontario, Canada between September 25, 2016, and September 26, 2020, was used in this study.

The researchers looked at the numbers of new cancers diagnosed each week during this time period. They compared the weeks before March 15, 2020 (the start of the COVID-19 pandemic) versus after March 15, 2020. The start of the pandemic was set as March 15, 2020, because that was the date when many Ontario doctors’ offices closed to in-person visits and dedicated cancer screening programs were shut down (they remained closed through May 1, 2020). They looked at the overall number of people who were diagnosed with any type of cancer, as well as the numbers of people with different specific types of cancer, including melanoma.

To see whether some groups of people may have been affected more than others, the researchers also determined whether the group of people diagnosed with cancer during the COVID-19 pandemic was different from the group diagnosed before the pandemic. They looked at factors including age, being male or female, being an immigrant, having other medical conditions, economic status, and where they lived (region of Ontario and rural or urban environment).

What were the main findings?

Immediate drop in cancer detection from March 2020, with a slow recovery through September 2020.

There was an immediate 34% drop in the average number of new cases of cancer diagnosed per week at the start of the COVID-19 pandemic (March 15, 2020) compared with before the pandemic. While this number increased over time, the recovery was slow through September 26, 2020 with only about 1% improvement per week. The number of new cancers diagnosed per week had not caught up to pre-pandemic levels by September 26, 2020. Overall, the researchers estimate that 12,601 cancers went undetected from March 15 to September 26, 2020. Melanoma was particularly impacted (see below).

As a whole, the group of people diagnosed with cancer during the COVID-19 pandemic was similar to the group diagnosed before the pandemic in terms of characteristics like age, gender, economic status, and where they lived. This finding means that the effect of the pandemic on missed diagnoses was similar in people with different backgrounds and characteristics, with no particular group being impacted more than others.

Drops in diagnoses were seen both for cancers that have organized preventative screening programs in Ontario (breast, cervical, colorectal and lung cancers) and those that are not typically screened for as a part of an organized program (like melanoma).

Melanoma was particularly impacted.

Along with cervical, endocrine, and prostate cancer, melanoma was one of the cancers that most commonly went undetected during the COVID-19 pandemic. There was a 54.6% drop in the average number of new cases of melanoma reported per week after the start of the COVID-19 pandemic. To put it another way, before the pandemic, an average of 71 people had their first melanoma diagnosis in Ontario each week. After March 15, 2020, the researchers estimated that melanoma went undetected in more than half of them – 38 people each week. Between March 15, 2020, and September 26, 2020, the total number of melanomas that were ‘missed’ added up to 1,056 people.

Why did the number of cancer diagnoses drop so dramatically during the COVID-19 pandemic?

While a drop in new cancers might sound like a good thing, the results of the study do not mean that fewer people had cancer during the COVID-19 pandemic. Instead, the results signal that fewer cancers were detected, and likely that more cancers went undetected.

At the start of the COVID-19 pandemic, the public was encouraged to avoid overburdening the health system, restrictions were in place, and many physician’s offices and screening programs were shut down. The researchers in this study did not specifically look at the reason for the drop in the number of cancers reported. However, the most likely explanation is that people waited to seek care for their medical concerns after the start of the COVID-19 pandemic. Compared with the number of people diagnosed with cancer, few people in Ontario died from COVID-19, so it is not likely that the ‘missing’ cancer cases represent people who died from COVID-19 before being diagnosed with cancer.

This means that there is likely to be a ‘backlog’ of cancers that were missed during the early months of the COVID-19 pandemic and have yet to be diagnosed. The number of cancers detected per week had not caught up to the pre-COVID-19 level by September 2020. To close this gap, it is important for people with new symptoms to see their physicians as soon as possible and to attend preventative cancer screenings.

These results are concerning because many cancers could be diagnosed after a delay, during which time the cancer could progress, decreasing the likelihood of cure. For example, most people with early stage melanoma can be cured with surgery, but surgery alone is not often effective once the melanoma has spread to other parts of the body.

It should be kept in mind that this was only one study in one region (Ontario, Canada). Additional studies in other countries with different healthcare systems, COVID-19 polices and COVID-19 infection rates would be helpful. Despite this, the main conclusions from this Canadian study are useful to understand how the COVID-19 pandemic may have caused missed cancer diagnoses in other regions including the U.S.

For more information
The article by Antoine Eskander and colleagues that describes this study was published in March 2022 in the Journal of the National Comprehensive Cancer Network. The article is titled “Incident Cancer Detection during the COVID-19 pandemic” and it is available online at: