Predictive role of [18F]FDG-PET early evaluation in patients (pts) undergoing preoperative chemotherapy (PCT) for breast cancer (BC).

Abstract

635 Background: Pathologic complete response (pCR) and minimal residual disease (pMRD) after PCT for BC correlate with a good prognosis. Early identification of pts who will achieve pCR/pMRD or who will not, could change the therapeutic strategy. The role of [18F]FDG PET in the prediction of pathological response in this clinical setting remains unclear. Methods: Pts with newly diagnosed early and locally advanced BC were submitted to 6-8 cycles of anthracycline and taxane-based PCT and there after operated. Pathological response was assessed according to Miller and Payne's classification. Pts with pCR or pMRD in the tumour and absence of cancer cells in ipsilateral axillary nodes were defined as having obtained an optimal pathological response (pR), while all the other conditions were classified as pathological nonresponse (pNR). [18F]FDG-PET/CT scan was included in the baseline work-up and repeated after 2 cycles of chemotherapy. Maximal standardized uptake value (SUVmax) was measured at the breast tumor and at the ipsilateral axilla and its percentage change (Δ-SUV) after 2 cycles was compared with the pathological response. Results: Out of forty-one pts, 10 (24%) achieved pR (5 pCR and 5 pMRD). With Δ- SUV reduction cut off of 50% sensitivity, specificity, negative predictive value and positive predictive value in order to identify pR were 100%, 26%, 100% and 30%, respectively. Thirty-three pts (80%) presented Δ-SUV reduction > 50% including all 10 pts with pR and 23 pts with pNR. On the contrary, all 8 pts with Δ-SUV reduction ≤ 50% presented pNR. All these 8 pts had ER+ tumors. Hence, out of a total of 24 pts with ER+ tumors, one third was correctly identify early as pNR. Conclusions: After 2 cycles of PCT, [18F]FDG-PET has a too high rate of false positive results to be recommended as standard predictor of pR. However, it could have a role in early identification of pts with ER+ tumours not candidate to obtain optimal pathologic response. No significant financial relationships to disclose.