Understanding Fibroglandular Tissue
Fibroglandular tissue refers to the functional breast tissue composed of glandular elements (milk-producing lobules and ducts) and supporting fibrous connective tissue that appears dense on mammography and affects both breast cancer risk and imaging sensitivity.
Composition and Characteristics
Fibroglandular tissue is distinguished from fatty tissue in the breast and has several important characteristics:
- It consists of milk-producing glandular structures (lobules and ducts) and supporting fibrous connective tissue 1
- It appears as dense white areas on mammography, contrasting with the dark appearance of fatty tissue 1
- The amount varies significantly between women and can change over time due to:
- Age (typically decreases with increasing age)
- Hormonal status (increases during pregnancy and lactation)
- Weight changes
- Use or withdrawal of endocrine therapy 1
Clinical Significance
Breast Density Classification
Fibroglandular tissue is the basis for breast density classification using the BI-RADS 4-category scale:
- Category A: Breasts are almost entirely fatty
- Category B: Scattered areas of fibroglandular density
- Category C: Heterogeneously dense breasts
- Category D: Extremely dense breasts 1
Approximately 43% of women aged 40-74 years in the US have heterogeneously or extremely dense breasts, with the highest proportion among women aged 40-49 years 1.
Impact on Breast Cancer Risk
Breast density is an independent risk factor for breast cancer:
- Women with heterogeneously dense breasts have a relative risk of 1.2 compared to average breast density 1
- Women with extremely dense breasts have a relative risk of 2.1 compared to average breast density 1
- Both fibroglandular tissue and breast fat tissue have independent effects on breast cancer risk 2
Impact on Imaging and Screening
Increased breast density significantly affects mammography performance:
- Reduces mammographic sensitivity from 87% in the lowest density category to 63% in the highest density category 1
- Reduces specificity from 96% to 90% as breast density increases 1
- May obscure small lesions, particularly in younger women and during pregnancy 1
- Increases the risk of false-positive findings at baseline screening 3
Imaging Considerations
Different imaging modalities visualize fibroglandular tissue differently:
- Mammography: Appears as white areas that can mask underlying abnormalities 4
- Digital Breast Tomosynthesis (DBT): Helps decrease the "masking effect" of dense tissue by providing 3D information 1
- Ultrasound: Shows fibroglandular tissue as hypoechoic areas with varying echogenicity 1
- MRI: Can accurately quantify fibroglandular tissue volume and distinguish it from fat 5, 6
Clinical Implications for Screening
For women with dense breasts (heterogeneously or extremely dense fibroglandular tissue):
- Supplemental screening options may be considered due to decreased mammographic sensitivity
- Digital Breast Tomosynthesis (DBT) may be particularly beneficial as it helps overcome the masking effect of dense tissue 1
- Restricting screening to only women with dense breasts would miss approximately 66% of potentially screen-detected cancers 1
Measurement and Quantification
Fibroglandular tissue can be measured through:
- Visual assessment by radiologists using BI-RADS categories
- Automated tools based on deep learning for quantitative measures 3
- MRI-based volumetric assessment, which correlates well with mammographic density (correlation coefficient of 0.91) 5, 6
Understanding fibroglandular tissue composition is essential for proper breast cancer risk assessment and for determining the most appropriate screening strategies for individual women.