In the early months of the pandemic, hospitals and other health-care facilities delayed or canceled elective procedures, including mammograms. As a result, the number of screening and diagnostic mammograms given to U.S. women fell by as much as 80 percent, the researchers found. In addition, many women with early stage breast cancer experienced delayed or reduced treatments, including chemotherapy.

The researchers predicted the longer term effect of these disruptions during the first six months of the pandemic by analyzing data representing 10 million women nationwide. Aside from skin cancers, breast cancer is the most common cancer affecting American women, with 1 in 8 of them developing breast cancer at some point in their life. Guidelines suggest that women start getting an annual mammogram in their early 40s, switching to a screening every two years at age 55.

Breast cancer is also a leading cause of cancer death in women, second only to lung cancer. Before the pandemic, the death rate for breast cancer in the United States had been declining, generally attributed to increased screening and better treatments. The new research urges women who had screenings or treatment delayed in 2020 to not delay further, noting that the projected number of additional deaths by 2030 could be two to four times greater if disruptions persist in health care.