Background Parenchymal Enhancement during Active Lactation: A Longitudinal Intra-Individual Breast MRI Study

Background

Breast MRI exams during lactation are often characterized with marked background parenchymal enhancement (BPE), complicating interpretation. When scheduling screening MRI in high-risk lactating patients, it remains unclear whether to defer MRI until presumed BPE declines; whether BPE meaningfully decreases during ongoing lactation remains uncertain.

Purpose

To evaluate intra-individual longitudinal change in BPE across consecutive breast MRIs performed during uninterrupted continuous lactation and assess whether deferring MRI during lactation is likely to reduce BPE.

Materials and Methods

In this retrospective single-center study (January 2017–July 2026), an internal radiologic search engine identified breast MRI reports containing lactation-related terms. Eligible patients had at least two consecutive contrast-enhanced breast MRIs during ongoing lactation; exclusions included history of breast cancer, post-lactation examinations, concurrent hormonal therapy, non-contrast MRI, and interscan interval under 3 months. BPE [BI-RADS minimal (0), mild (1), moderate (2), marked (3)] was abstracted from clinical reports. The primary outcome was within-patient change in BPE category (ΔBPE) between consecutive MRIs; interscan interval was recorded. Analyses were descriptive.

Results

Nineteen women met inclusion criteria, contributing 20 discrete lactation episodes (mean age 32 years). Indications were predominantly high-risk screening, with most patients carrying BRCA pathogenic variants. The mean interscan interval was 9.55 months during uninterrupted lactation. Baseline BPE during lactation was predominantly marked (n=19/20, 95%), or moderate (n=1). Intra-individual BPE showed minimal net change over time: most patients remained in the same BPE category between examinations (n=17), with minority of cases showing increases (n=1) or decreases over time (n=2) by one category. Overall, no consistent decline in BPE with longer interscan intervals was observed (p=0.93). No breast cancers were diagnosed between or shortly after the paired MRIs.

Conclusion

During approximately 10 months of continued lactation, BPE remained largely stable. Routine deferral of breast MRI solely to await a reduction in BPE appears unwarranted.