"Are changes in breast density during the menstrual cycle relevant? To what?"

Area of Science:

• Radiology and Imaging
• Oncology
• Women's Health

Background:

• High breast density (BDen) can mask cancers, creating a masking effect (ME).
• Breast density is a modifiable breast cancer risk (BCR) factor.
• Understanding BDen variability is crucial for accurate cancer detection and risk assessment.

Purpose of the Study:

• To quantify changes in glandular volume (GVol), breast volume (BVol), and BDen throughout the menstrual cycle.
• To assess if these cyclic changes influence the masking effect (ME).
• To determine the relevance of these changes for interventional studies targeting BCR reduction using these parameters.

Main Methods:

• Analysis of 39,997 mammograms from 19,904 premenopausal women using photon counting technique.
• Data categorized by women's age and week of the menstrual cycle relative to the first day of the last menses (FDLM).
• Cyclical variations in GVol, BVol, and BDen were assessed across the 4 weeks of the menstrual cycle.

Main Results:

• All measured parameters (GVol, BVol, BDen) exhibited cyclical variations during the menstrual cycle.
• Mean inter-week differences were generally small but increased with age.
• Younger women showed potentially significant inter-week variations: >10% for BDen, >15% for GVol, and >50% for BVol.

Conclusions:

• Direct impact of small mean BDen changes on the masking effect (ME) is unlikely.
• Significant menstrual cycle-related variations in younger women could confound results of interventional studies.
• Accounting for menstrual cycle phase is recommended for studies investigating BDen, GVol, or BVol to reduce breast cancer risk (BCR).