Purpose: To investigate the value of response monitoring in both the primary tumour and axillary nodes on sequential PET/CT scans during neoadjuvant chemotherapy (NAC) for predicting complete pathological response (pCR), taking the breast cancer subtype into account.
Methods: In 107 consecutive patients 290 PET/CT scans were performed at baseline (PET/CT1, 107 patients), after 2 - 3 weeks of chemotherapy (PET/CT2, 85 patients), and after 6 - 8 weeks (PET/CT3, 98 patients). The relative changes in SUVmax (from baseline) of the tumour and the lymph nodes and in both combined (after logistic regression), and the changes in the highest SUVmax between scans (either tumour or lymph node) were determined and their associations with pCR of the tumour and lymph nodes after completion of NAC were assessed using receiver operating characteristic (ROC) analysis.
Results: A pCR was seen in 17 HER2-positive tumours (65 %), 1 ER-positive/HER2-negative tumour (2 %), and 16 triple-negative tumours (52 %). The areas under the ROC curves (ROC-AUC) for the prediction of pCR in HER2-positive tumours after 3 weeks were 0.61 for the relative change in tumours, 0.67 for the combined change in tumour and nodes, and 0.72 for the changes in the highest SUVmax between scans. After 8 weeks equivalent values were 0.59, 0.42 and 0.64, respectively. In triple-negative tumours the ROC-AUCs were 0.76, 0.84 and 0.76 after 2 weeks, and 0.87, 0.93 and 0.88 after 6 weeks, respectively.
Conclusion: In triple-negative tumours a PET/CT scan after 6 weeks (three cycles) appears to be optimally predictive of pCR. In HER2-positive tumours neither a PET/CT scan after 3 weeks nor after 8 weeks seems to be useful. The changes in SUVmax of both the tumour and axillary nodes combined correlates best with pCR.