Abstract P5-02-09: Ki67-labelling index of luminal breast cancers: Agreement of core biopsy and surgical specimen results

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Abstract Objective: To highlight the agreement between Ki67-Labelling indices (LIs) of core biopsies (CB) and related surgical specimens (SSP) in luminal breast cancers (BCs) adopting the recommendations of the St Gallen Consensus Conference 2013 and the International Ki67 In Breast Cancer Working Group. Methods: We investigated CBs and the related SSPs of 220 luminal Her2 negative BCs. To assess the Ki67-LI a total of 510 tumour cells including hot spot, cold spot and an area of intermediate proliferation was counted by one observer. Every positive nucleus was counted, independent of the staining intensity. A Ki67-LI cut-off <20% as recommended by the St Gallen Consensus was used to define luminal A BCs. Agreement between CB and SSP, rates of under- and overestimation, and positive predictive values (PPV) of CB based subtyping (luminal A vs. B) were calculated. Results: In SSP 140/220 BCs (64%) were luminal A, 80 (36%) were luminal B. The agreement between CB and OP was 77% (169/220). Overestimation of proliferation in CB occurred in 10 (4%) and underestimation in 41 (19%) cases. The PPVs of CB based Ki67-LI for luminal A and luminal B were 0.76 (130/171) and 0.79 (39/49), respectively. Conclusion: The agreement of CB and SSP based subtyping of luminal BCs is generally high. However, underestimation of proliferation in CB may result in subtype misclassification in almost one fifth of luminal Her2 negative luminal tumours. Citation Format: Cornelia M Focke, Thomas Decker. Ki67-labelling index of luminal breast cancers: Agreement of core biopsy and surgical specimen results [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-02-09.