Assessment of Response to Neoadjuvant Therapy for Breast Cancer
MRI is the most accurate and recommended imaging modality for assessing response to neoadjuvant therapy for breast cancer, followed by ultrasound and mammography/digital breast tomosynthesis. 1, 2
Recommended Imaging Protocol
Before Starting Neoadjuvant Therapy
- Obtain baseline imaging with multiple modalities to accurately document initial disease extent:
During Neoadjuvant Therapy
- Early response evaluation should be performed 6-9 weeks after treatment initiation to:
After Completion of Neoadjuvant Therapy
- Comprehensive imaging assessment using:
- MRI with contrast (highest recommendation, rating 9/9) - most accurate for residual disease assessment 1, 2
- Breast ultrasound (rating 8/9) - particularly reliable for tumors >7mm 1
- Diagnostic mammography or digital breast tomosynthesis (rating 7/9) - especially for masses well visualized on pre-treatment mammogram 1
Accuracy of Different Imaging Modalities
MRI
- Most accurate modality for assessing residual tumor size (63% accuracy) 3
- Superior for detecting multifocal disease (correctly identified in 12/15 cases) 3
- Particularly valuable for invasive lobular cancers and higher-grade lesions 1
- Findings strongly correlate with pathological response 2
Ultrasound
- Second most accurate modality (38-82% accuracy) 4, 3
- Early response on ultrasound associated with 2.9 times higher chance of pathologic complete response 5
- Contrast-enhanced ultrasound shows promise for early response assessment through evaluation of tumor vascularity changes 6
Mammography/Digital Breast Tomosynthesis
- Accuracy ranges from 43-89% 4, 3
- Less reliable for dense breasts and invasive lobular cancers 2
- Digital breast tomosynthesis may improve visualization compared to standard mammography 2
Response Evaluation Criteria
- Complete response (CR): Disappearance of tumor entirely 2
- Partial response (PR): ≥30% decrease in longest tumor diameter 2
- Stable disease: No significant change in tumor size 2
- Progressive disease: ≥20% increase in longest tumor diameter 2
- Pathologic complete response (pCR) is associated with better overall survival 2
Important Caveats and Limitations
- No single imaging modality can reliably detect all residual disease after neoadjuvant chemotherapy 1
- Post-treatment imaging correctly estimates pathological tumor size within 5mm in only 43-46% of cases 5
- Surgical excision remains necessary as the definitive method to determine pathologic response 4
- Tumor subtype affects imaging accuracy - lobular cancers are particularly challenging to assess 2
- Post-treatment lymph node status is one of the most important prognostic factors 2
- Response patterns vary (concentric shrinkage vs. tumor fragmentation), affecting measurement accuracy 2
Special Considerations
- For ambiguous results, multicentric disease, or invasive lobular cancers, contrast-enhanced MRI is particularly helpful 2
- FDG-PET may predict pathologic response at 2-3 months after chemotherapy initiation 2
- Combining FDG-PET and MRI for response evaluation can be complementary 2
- Patients with early clinical response derive most benefit from non-cross-resistant regimens 2
- For patients with insufficient early response or progressive disease, consider switching treatment 2
Despite advances in imaging technology, surgical excision with pathological assessment remains the gold standard for determining complete response to neoadjuvant therapy 4, 5.