TOPLINE:
A new analysis found that the incidence of interval breast cancers diagnosed in screened patients has increased over an almost 30-year period, but the proportion of interval cancers vs screen-detected cancers has remained steady at about 30%. Factors associated with an increased risk for interval cancer included a family history of breast cancer, dense breasts, and use of hormone replacement therapy.
METHODOLOGY:
- Interval cancers are diagnosed between screening rounds because the cancer was missed at screening or because the cancer was aggressive and developed rapidly. Although it’s well known that breast cancer diagnoses have increased over time, it’s less clear how many are interval (vs screen-detected) cancers and what factors can help identify patients at greater risk for interval cancer.
- A population-based cohort study included 527,144 women who were cancer-free and were aged 40-74 years, who were invited for mammography screening in Stockholm between 1989 and 2020; among them, 58,111 were included in the mammographic density analysis. Screening occurred every 18-24 months.
- Researchers analyzed the family history of cancer and other factors, such as breast density, age at first childbirth, education level, and use of hormone replacement therapy.
- Primary outcomes were diagnoses of screen-detected and interval cancer. Researchers tracked both over the 30-year study period to determine the incidence of each, as well as the proportion of interval cancers vs screen-detected in the context of total diagnoses.
TAKEAWAY:
- Overall, 5.5% in the cohort were diagnosed with breast cancer. Among them, 2.0% had screen-detected cancer and 0.8% had interval cancer. Although the incidence of interval breast cancer increased over time, the proportion of interval cancer remained around 30% throughout the study period. The proportion was higher (40%) among younger women who were aged 40-49 years and lower (23%) among those aged 60-74 years.
- Having a family history of breast cancer was associated with an increased risk for interval cancer (hazard ratio [HR], 1.85). This risk for interval cancer was more pronounced for those with a family history of interval cancer (HR, 2.92) vs screen-detected cancer (HR, 1.70), as well as in those with a family history of ovarian, melanoma, colorectal, prostate, and testicular cancers.
- Higher mammographic density was associated with an increased risk for both interval and screen-detected breast cancers. The risk for interval cancer increased with greater breast density (compared with the lowest density category).
- Older age at first childbirth (HR, 1.36), higher education level, and use of hormone replacement therapy (HR, 1.35) were associated with an increased risk for interval cancer. About half of estrogen receptor (ER)–negative cases were interval cancers vs less than 30% among ER-positive cases.
IN PRACTICE:
“The proportion of [interval cancer] was not reduced during the past three decades in Sweden,” the authors wrote. Women with a family history of breast cancer “may be at higher risk of developing [interval cancer], often due to the rapid growth of tumors between screening intervals rather than missed detections.”
“Identifying patients at high risk of poor breast cancer outcomes despite routine mammography screening is a critical goal for the breast cancer screening community. More efforts are needed to advance the field of risk prediction by leveraging information beyond traditional risk factors, applying cutting-edge AI [artificial intelligence] technology, and targeting end points correlated with breast cancer prognosis to achieve greater reductions in breast cancer mortality,” the authors of an invited commentary wrote.
SOURCE:
This study, led by Yuqi Zhang, PhD, Department of Medical Epidemiology and Biostatistics, Karolinska Institutet in Stockholm, Sweden, was published online in JAMA Oncology, alongside an invited commentary.
LIMITATIONS:
The findings were based on the screening setting in Sweden, where screening intervals and practices are standardized, potentially limiting the findings’ generalizability to other settings with different protocols. Information on hormone replacement therapy was only available from 2005, which might have resulted in lower estimates than the numbers in earlier periods when its use was more prevalent.
DISCLOSURES:
This study received support through grants from the Swedish Research Council; Swedish Cancer Society; Stockholm County Council; and Cancerföreningen, Stockholm. The authors reported no relevant conflicts of interest.
This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.