Background and aim: (99m)Tc-Sestamibi (MIBI) scintimammography has an established role in the diagnosis of breast cancer. As a functional imaging technique, it may also be useful in assessing the response to chemotherapy. The aim of this study was to assess the effectiveness of the technique for this purpose.
Methods: Twenty-six patients undergoing neoadjuvant chemotherapy for large or locally advanced breast cancer were monitored using the tumour to background ratio measured on MIBI scintimammograms. Patients were assessed and the size of the tumour was measured by callipers and ultrasonography before and at the end of treatment. Patients were assessed as complete, partial or non-responders. Following chemotherapy, patients proceeded to surgery with pathological evaluation of the operative specimen.
Results: Twenty-four of the 26 patients showed a reduction in MIBI uptake on completion of chemotherapy. Residual tumour was demonstrated on the scintimammogram in four patients and all had significant residual disease on histology. In the remaining 22 patients, the final scintimammogram was negative, although three patients were assessed as non-responders and had large residual tumours on histology.
Conclusion: A positive MIBI scan is highly predictive of the presence of significant residual disease on completion of chemotherapy. However, a negative MIBI scan does not rule out the presence of considerable residual tumour. Whereas ultrasound and clinical assessment may underestimate the response to chemotherapy, MIBI imaging tends to overestimate the response.