Unique Traits for Interval Breast Cancers Point to Poor Patient Outcomes

Interval breast cancers (IBCs) – those that appear during the year between a patient’s screening appointments – could have particular features that make them more aggressive and malignant, a new study has found.

In an article published in the June 30 JAMA Network Open, investigators from Oregon State University revealed the results of their 19-year, nearly 5,500-woman study during which they followed women who received regular screening mammograms. According to their findings, cancers diagnosed within a year of a negative mammogram shared several common traits that point to potential negative outcomes for the patient.

Based on those characteristics, the team said, it is likely that IBCs have unique facets that mean providers should implement alternative screening strategies.

“Interval cancers occurring within one year from a mammogram with negative results may have a unique biology that accounts for aggressive features,” wrote the research team, led by Veronica Irvin, Ph.D., assistant professor of public health and human sciences at Oregon State University. “Women with IBCs diagnosed within one year of negative mammogram results overall were associated with worse survival than women with breast cancers detected by screening.”

To make this determination about IBCs and outcomes, Levin’s team examined mammography, tumor characteristics, and demographic data from patients enrolled in the Women’s Health Initiative (WHI), a longitudinal cohort study of post-menopausal women. Of that group, the team examined data from women, between the ages of 50 and 79, who were enrolled in one of 40 clinical locations between 1993 and 1998. They, then, followed the women for an average of 19 years.

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Investigators divided the study group into two cohorts. One underwent mammography every 2.5 years while the other received yearly scans. The women included in this study, according to the team, had no personal breast cancer history and no suspicious findings on their baseline screening mammogram.

According to the investigators, 3,019 women developed breast cancer during the study – approximately 65 percent of which was diagnosed at screening. The other 35 percent were diagnoses of IBC. And, those IBC cancers were very different from the ones caught on routine screening. They had significantly more lobular histologic characteristics, had a larger tumor size, involved the lymph nodes, and were identified at a later clinical stage.

In addition, the team reported, women who received IBC diagnoses were also more likely to die than those women who had cancer detected at screening. And, adjusting for known breast cancer risk factors, histologic type, waist-to-hip ratio, molecular subtype, lymph node involvement, tumor size, or intervention group did not mitigate that higher mortality risk.

It is important to note, the team said, that they found no significant difference in the tumor traits or patient outcomes for IBCs identified after one year. That result, they said, indicates that IBCs likely have characteristics that set them apart from other forms of breast cancer.

“The unique findings from our study are that IBCs that emerge within one year after negative mammogram results might have distinct tumor characteristics that identify them as at a particularly high risk for metastasis,” the team said.

Consequently, these findings have several clinical implications, they added. Women who have breast cancer symptoms and a negative screening mammogram should be either recalled more frequently or they should have a shorter screening period. In addition, they could also undergo supplemental ultrasound screening or have an MRI. Genomic testing can also play a role in helping providers distinguish between indolent and aggressive breast cancers.

Overall, these results contribute to a greater understanding of breast cancer and how it can be treated more successfully, the team said.

“This study adds to a growing body of literature that argues for the development of novel approaches to detect life-threatening cancers currently missed by mammographic screening,” the team wrote.