Cut-off analysis and prognostic relevance of Ki67 for resected early stage pure invasive lobular breast carcinoma (ILC).

544Background: In clinical practice, the prognostic potential (and best cut-off) of Ki67 for pure ILC is usually borrowed from the ductal histotype, though a formal validation has not yet been fully established. Thus, the aim of this analysis was to investigate the best prognostic cut-off value of Ki67 and its long-term impact assay in a multi-center series of patients affected by early stage pure ILC. Methods: Clinical-pathological data of consecutive patients affected by pure ILC undergone surgery between January 1990 and December 2013, diagnosed at 2 Italian institutions, were retrospectively correlated with overall survival and disease-free survival (OS/DFS) using a Cox model. The maximally selected Log-Rank statistics analysis was applied to the Ki67 continuous variable to estimate the appropriate cut-off. Kaplan-Meier curves were compared with Log-Rank analysis. Internal cross-validation was accomplished. Results: Data from 457 pts were gathered (median age 61 years [yrs], range 35-96 yrs). At media...