Calling fewer women back for more testing after a suspicious mammography finding is associated with higher rates of breast cancers found between screenings.

These “interval” cancers also tend to occur more often in older women, according to the results of a new study by the University of Wisconsin School of Medicine and Public Health (SMPH). Published online this week in the journal Radiology, the study suggests that establishing a minimum recall rate is a reasonable and potentially important goal for breast cancer screening programs.

“Our research suggests that a minimum threshold for recall is an important safeguard against missing breast cancers that would otherwise be diagnosed later by the patient or her doctor,” said Elizabeth Burnside, MD, MPH, professor of radiology. “But we also know that recalls have a downside, including anxiety for the patient and additional expenses to the health-care system. While we acknowledge that different patient populations may not face the same potential tradeoffs between lower recall rates and interval cancers, our study provides convincing evidence that establishing a lower threshold for recall rate is warranted.”

Breast cancer screening programs routinely specify maximum recall rates after screening mammography, but no such consensus currently exists for a minimum recall rate, below which additional cancers would be missed. In the United Kingdom, where the data for this study were collected, the established maximum recall-rate target is less than 7% for a patient’s first screening (also known as a prevalent screen) and less than 5% for incident screens (those in which previous screening results exist).

For the study, Burnside and colleagues analyzed 5.1 million screening episodes from 84 facilities in the UK National Health Service Breast Screening Program (NHSBSP). A screening period is defined as the period during which a set of breast screening activities for an eligible woman takes place. Data were drawn from a 36-month period with a 3-year follow-up in women ages 50 to 70 years.

Recall rate averaged 4.56%, with an interval cancer rate of 3.1 per 1,000 women screened. Interval cancers are associated with a worse prognosis than screen-detected cancers.

Lower recall rates correlated with higher interval cancer rates. The researchers estimated that, in aggregate, 80 to 84 additional recalls would be required to avoid one interval cancer, a ratio that varied based on age group and prevalent screens vs incident screens. Screening mammography outcomes based on age showed that both cancer detection rates and interval cancer rates were lower in younger age groups. That is as expected based on underlying breast cancer incidence according to age.

“Recall rate had more of an impact on interval cancer in patients who are older,” said Burnside. “The lower number of recalls required per interval cancer avoided in older women and incident screens as compared to younger women and prevalent screens, respectively, shows a slightly different ‘value’ in terms of the tradeoff between recall rate and interval cancers.”

While the study focused on the UK NHSBSP alone, Burnside says the methods used provide a basis for other programs to determine a minimal recall-rate threshold that maximizes value for women undergoing screening.

The study also underscores the crucial importance of comprehensive, accurate data collection of interval cancers in screening programs like the system in the UK.

“A big-picture lesson in our study is the power of rigorous quality-assurance infrastructure to help breast cancer screening programs learn from actual practice and use that information to make informed programmatic decisions for the future,” said Burnside. “This study documents the benefit of carefully tracking mammography use and outcomes as achieved in the NHSBSP.”

Additional research will help determine a specific minimum threshold for recall rate and assess the impact of digital mammography on the relationship between recall rate and interval cancers.