Breast Density Categories — BI-RADS 2013
| Category | Label | Fibroglandular % | Sensitivity | Supplemental Screening |
|---|---|---|---|---|
| A | Almost entirely fatty | <25% | ~90% | Routine mammography sufficient |
| B | Scattered fibroglandular | 25–50% | Slightly reduced | Routine mammography; supplement if other risk factors present |
| C | Heterogeneously dense | 51–75% | Reduced | Discuss supplemental US or MRI with patient |
| D | Extremely dense | >75% | Significantly reduced | Supplemental screening recommended (US or MRI) |
FDA MQSA Amendment — Effective September 10, 2024: All mammography reports must include breast density category. All patients with Category C or D density must receive standardized notification language informing them that dense tissue may make it harder to evaluate results and may be associated with increased cancer risk. Non-compliance carries regulatory consequences.
Screening Recommendations by Risk Group (ACR/SBI)
| Risk Group | Definition | Recommendation | Start Age |
|---|---|---|---|
| Average risk | No personal history of BC, no known high-risk mutation, no prior chest RT, <15% lifetime risk | Annual mammography (ACR/SBI). ACS: shared decision ages 40–44, annual 45–54, biennial 55+. USPSTF 2024: biennial starting age 40. | 40 |
| Dense breasts (C or D) | Heterogeneously or extremely dense | Annual mammography continues; consider supplemental US (annual) or MRI if additional risk factors | 40 |
| Elevated risk (15–20% lifetime) | Strong family history, intermediate-risk models (Tyrer-Cuzick 15–20%) | Annual mammography + consider supplemental MRI | 40, or 10 years before youngest affected relative |
| High risk (≥20% lifetime) | BRCA1/2, untested first-degree relative of BRCA carrier, ≥20% by validated model, Li-Fraumeni, Cowden/PTEN, Bannayan-Riley-Ruvalcaba | Annual MRI + annual mammography, staggered 6 months apart | 25–30 (BRCA); 10 years before youngest affected relative |
| Prior chest radiation | Mediastinal/chest RT ≥30 Gy before age 30 | Annual MRI + annual mammography | 8 years post-RT or age 25, whichever is later |
| Personal history of BC | Prior ipsilateral or contralateral breast cancer | Annual mammography (bilateral or contralateral); consider annual MRI if dense breasts or elevated risk | At diagnosis; annual thereafter |
| Prior atypical biopsy | ADH, ALH, or LCIS on prior biopsy | Annual mammography; consider annual MRI. Chemoprevention discussion. | At time of diagnosis; annual thereafter |
High-risk screening timing: Annual MRI and annual mammography should be staggered approximately 6 months apart — not performed simultaneously — to maximize the interval between any two screening examinations. Both modalities detect cancers the other misses.
Risk Model Tools
Tyrer-Cuzick (IBIS) v8+ is the preferred model for determining high-risk screening eligibility — it includes both family history and personal risk factors. BRCAPRO and BOADICEA are alternatives.
Gail Model only includes first-degree relatives and does not adequately capture paternal lineage or BRCA risk — it underestimates risk in many high-risk families and should not be used alone to determine MRI screening eligibility.
Supplemental Screening Options
| Modality | Cancer Detection Added | False Positive Rate | Notes |
|---|---|---|---|
| Whole-breast US (WBUS) | ~4 per 1,000 screened | High (~10x vs mammography alone) | Alternative for intermediate-risk dense-breast patients when MRI is not feasible |
| MRI | ~10–16 per 1,000 in high-risk women | Lower than WBUS | Preferred for ≥20% lifetime risk; stagger with mammography by 6 months |
| Contrast-Enhanced Mammography (CEM) | Approaches MRI for invasive cancer | Intermediate | Useful when MRI contraindicated; not yet standard-of-care but recognized by ACR |
| Abbreviated MRI (AB-MRI) | Equivalent to full protocol for invasive cancer | Intermediate | 3–5 min scan time; emerging for intermediate- and high-risk patients |