How to manage a patient with metastatic breast cancer (MBC) and conflicting imaging results, with computed tomography (CT) scans showing multiple bone metastases (mts) but bone scintigraphy showing no metastatic lesions?

Management of Metastatic Breast Cancer with Conflicting Imaging Results

When CT shows bone metastases but bone scintigraphy is negative, trust the CT findings and proceed with treatment for metastatic breast cancer with bone involvement, as CT can better distinguish osteolytic, sclerotic, and soft tissue lesions. 1

Understanding the Discrepancy Between Imaging Modalities

The conflicting results between CT and bone scintigraphy can be explained by the different mechanisms of these imaging techniques:

• Bone scintigraphy (bone scan):

  • Detects increased osteoblastic activity rather than the tumor itself
  • Has moderate sensitivity (96%) but low specificity (66%) 2
  • May miss purely osteolytic lesions that lack osteoblastic response 1
  • False negatives can occur in rapidly growing aggressive lesions, small lesions, or purely lytic metastases 1

• CT scan:

  • Directly visualizes bone structure and lesions
  • Can readily distinguish between osteolytic, sclerotic, and soft tissue lesions 1
  • More effective at detecting lesions that extend into soft tissue 1
  • Higher specificity for characterizing bone lesions 1

Recommended Management Algorithm

1. Confirm metastatic disease:

   • Biopsy one of the metastatic lesions seen on CT to confirm diagnosis if not already done 1
   • Reassess biomarkers (ER, PgR, HER2) from the metastatic site 1

2. Additional imaging:

   • Consider PET-CT which may provide better assessment of bone-predominant metastases 1
   • MRI is more sensitive than bone scintigraphy and can be used to further characterize lesions 1
   • Consider hybrid imaging techniques like SPECT/CT for better anatomical correlation 1

3. Multidisciplinary discussion:

   • Present the case in a multidisciplinary tumor board as recommended for all metastatic breast cancer cases 1
   • Discuss the discrepancy between imaging modalities and the clinical implications

4. Treatment approach:

   • Initiate systemic therapy appropriate for the breast cancer subtype 1
   • Add bone-modifying agents (BMAs) such as bisphosphonates or denosumab, which are recommended for all patients with bone metastases regardless of symptoms 1
   • Consider orthopedic evaluation for significant lesions in long bones or vertebrae 1

5. Monitoring response:

   • Use the same imaging modality (CT) for follow-up to ensure comparability 1
   • Evaluate response every 2-4 months depending on disease dynamics 1
   • Consider PET-CT for earlier guidance in monitoring bone-predominant metastases 1

Bone-Specific Management

• Bone-modifying agents:

  • Start denosumab (administered every 4 weeks) or zoledronate (can be administered every 12 weeks in stable disease after 3-6 monthly treatments) 1
  • Denosumab is more effective than zoledronate in delaying skeletal-related events 1
  • Before starting BMAs, complete dental evaluation and prescribe calcium and vitamin D supplements 1

• Radiation therapy:

  • Consider for lesions at moderate risk of fracture or associated with moderate to severe pain 1
  • A single 8-Gy fraction is as effective as fractionated schemes for uncomplicated bone metastases 1

Common Pitfalls and Caveats

• Don't dismiss bone metastases based solely on negative bone scan: Purely lytic lesions may not show increased uptake on bone scintigraphy 1

• Beware of flare phenomenon: During the first few months of treatment, bone scans may show increased uptake due to healing response rather than disease progression 1

• Avoid overreliance on a single imaging modality: Each technique has strengths and limitations; correlation with clinical findings and multiple imaging modalities provides the most accurate assessment 1

• Consider the type of bone metastases: Breast cancer can cause osteolytic, osteoblastic, or mixed lesions, which may be detected differently by various imaging modalities 3