Prognostic and predictive impact of Ki-67 before and after neoadjuvant chemotherapy on PCR and survival: Results of the GeparTrio trial.

1023 Background: We previously reported as a result of the GeparTrio phase III trial that response-guided neoadjuvant chemotherapy (CT) with TACx8 or TAC/NX, compared to TACx6, can improve survival especially in hormone-receptor (HR)-positive tumors. As this benefit could not be predicted by pathological complete response (pCR), better surrogate response markers are warranted. Methods: 2072 patients with operable or locally advanced breast cancer were treated with 2 cycles TAC before interim response assessment. Responders were randomized to additional TACx4 or TACx6 and non-responders to TACx4 or NXx4. We centrally measured Ki-67 in1165 pre-CT core biopsies and in 676 post-CT surgical samples. Counting patients with a pCR as having 0% Ki-67, 757 pre-/ post-CT pairs were available. Ki-67 percentage levels were grouped to low (0-15%), moderate (15.01-35%), and high (35.01-100%) according to cut-point finding analysis in a training and validation cohort. Results: pCR rates were 4.2%, 12.9%, and 29.0% in tumors with low, moderate, and high pre-CT Ki-67 levels (p<0.0001). Pre-CT Ki-67 levels significantly predicted disease-free survival (DFS) (log rank p<0.0001) overall, in the HR+ (p<0.0001), but not in the HR- (p=0.5) subgroup. Post-CT Ki-67 levels correlated with DFS (p<0.0001). Patients with low post-CT Ki-67 levels showed comparable outcome to patients with pCR. Patients with increased Ki-67 levels from before to after CT showed an impaired outcome compared to patients with stable or decreased Ki-67 levels (p<0.0001). However, post-CT Ki-67 levels appeared to have more prognostic relevance than Ki-67 changes. Low post-CT Ki-67 levels were not more frequent after response-guided treatments (response-guided vs conventional: p=0.153; TACx6 vs TACx8: p=0.335; TACx6 vs TAC/NX: p=0.420). Similar negative results were found for HR+ and HR- subgroups. Conclusions: Pre-CT Ki-67 levels are predictive for pCR and prognostic for DFS. Post-CT Ki-67 levels and changes between pre-and post-CT-Ki-67 levels are prognostic for DFS. As neither could predict different treatment effects on DFS, Ki67 cannot replace pCR as a surrogate marker for outcome after neo-adjuvant CT.