Abstract Background and Aim: Reduction in FDG-PET uptake as response predictor after induction chemotherapy for breast cancer has been described. Our aim was to determine whether a SUV reduction ≥45% in the breast lesion could accurately predict pathological Complete Response (pCR). Material and Method: Stage II-IIIa breast cancer patients (p) with primary tumor ≥3cm or positive axilla were included provided they were amenable to neoadjuvant chemotherapy with Docetaxel-Doxorubicin-Cyclophosphamide (TAC). A FDG-PET scan was performed on day −1 of the first course and was repeated on day+8 of the same course. SUV-uptake differences (day 8 minus day −1) were correlated to the eventual pathological response according to Miller-Payne criteria. Results: 42p were included. Median age was 45 years (30-66). 11p (26.2%) were triple-negative tumors. 2p (4.8%) were Her-2 +. By stage, 13p (30.9%) were IIA, 17p (40.4%) IIB and 12p (28.2%) IIIA. 23p (54.7%) were N+ (FNAB positive). Median breast-SUV on first PET scan was 5.51 (1.3−18.50). 40p (95.2 %) completed the scheduled 6 courses. 41p (97.6%) were submitted to surgery. 11p (26.2%) achieved a pCR. 40p (95.2%) were evaluable for the primary objective. 1p (0.02%) died of disease progression before surgery and 1p (0.02%) with pCR could not be assessed by PET. 7 out of 14 p (50%) with uptake reduction ≥45% with respect to the basal value, and 3/26p (11.5%) whose reduction was <45% achieved a pCR (p=0.007). SUV decrease >45% accurately predicted 7/10 pCR (70%) that could be assessed. Conclusions: Our study confirmed the value of PET-SUV reduction on day 8th as an early predictor of pCR with neoadjuvant TAC chemotherapy. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-13-16.