149PD - Prognostic impact of proliferation for resected early stage breast cancer according to histology: Cut-off analysis of Ki67 in 859 patients with pure invasive lobular and ductal breast carcinoma (ILC/IDC)

Abstract

While the prognostic impact of Ki67 has been extensively investigated in IDC, despite the absence of standardized cut-off, its role in ILC has not been fully validated. Thus, the aim of this analysis was to investigate the prognostic potential of Ki67 in a multi-center series of patients (pts) affected by early stage pure ILC comparing with IDC. Clinicalpathological data of consecutive pts affected by pure ILC and IDC, referring to 2 institutions, were correlated with overall survival and disease-free survival (OS/DFS) using a Cox model. The maximally selected Log-Rank statistics (MSLRS) analysis was applied to the Ki67 continuous variable to estimate the appropriate cut-off according to histology. Data from 457 ILC and 402 IDC pts were gathered (median age 61/59 years [yrs]). At a median follow-up of 75 months, 10-yrs OS and DFS for ILC and IDC were 81.7%/83.4%, and 71.4%/76.2%, respectively. The MSLRS analysis identified 4% and 18% as optimal Ki67 cut-offs for OS for ILC and IDC, respectively. At the multivariate analysis Ki67, Performance Status (PS), nodal status (N), and TNM-tumor-size (T-size) were independent predictors for OS in ILC pts. Ki67 highly replicated at the internal cross-validation analysis. For IDC pts, PS, age, estrogen receptor expression and T-size were independent predictors for OS. With regard to DFS, the MSLRS analysis identified 4% and 14% as optimal KI67 cut-offs for ILC and IDC, respectively. PS and N were independent predictors for ILC, while PS, age, grading and T-size were predictors for IDC. Log-rank analysis is shown in the table:Tabled 1HistotypeKi675-yrs OS (%)10-yrs OS (%)Log-RankILC≤ 4%96.989.9p = 0.008> 4%90.177.2IDC≤ 18%97.495.8p = 0.002> 18%93.662.65-yrs DFS (%)10-yrs DFS (%)ILC≤ 4%88.279.4p = 0.03> 4%81.169.2IDC≤ 14%96.087.0p = 0.002> 14%89.261.8 Open table in a new tab Despite the retrospective and exploratory nature of the study, the prognostic relevance of Ki67 (as well as its optimal cut-off) seems to significantly differ according to histology. In particular, a very low cut-off of Ki67 (4%) may significantly discriminate the prognosis of pts with ILC.