Abstract PD06-05: St. Gallen 2011 clinico-pathological subtypes of breast cancer: concordance of core biopsies and related surgical specimens

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Abstract Rationale: Whereas the St Gallen International Expert Consensus on the Primary Therapy of Early Breast Cancer 2011 considered molecular typing as the adequate model representing the heterogeneity of breast cancers, it did not generally accept gene expression array criteria for clinical decision making. When the classification of tumours by gene expression array criteria and immunohistochemical analysis of ER, PR and HER2 are discrepant, patients should be managed according to the current immunohistochemical markers. Therefore, for systemic therapy decision the St Gallen consensus Conference 2011 did recommend clinicopathologically defined breast cancer subtypes (cpBCST) to guide therapeutic choices. There are many reasons to provide patients and doctors these information already preoperatively. To evaluate relevance of St. Gallen 2011 cpBCST core biopsy (CB) results we estimated their concordance with postoperative cpBCSTs. Methods: cpBCSTs of CB and related surgical specimen (SSP) of 379breast cancers (BC) (62 Grade 1, 157Grade 2, 160 grade 3) were assessed according to the St Gallen definition using the prospectively estimated results for Estrogen, Progesteron, and Her2-status. To differentiate between Luminal A and the Her2 negative subgroup of Luminal B we retrospectively measured the mitotic activity index (MAI) with a cut-off of ≥10 for high versus low as evaluated by Baak et al. 2008. Concordance between cpBCST results of CB and SSP and PPV of cpBCST of CB were calculated. Results: None of the Luminal A BCs was overestimated in CB, whereas 49% (53/108) of all Luminal B or 66% (55/83) of the Luminal B (Her2−) BCs were underestimated as Luminal A, for all other subtypes, the agreement was 100%. In general, there was no overestimation as a more unfavourable CPBCST in CB. The overall underestimation rate came out with 14%. Whereas the PPV in CB is 100% for Luminal B, Her2 positive, and Triple negative CPBCSTs, it is only 78% for Luminal A (198/254). The reason is underestimation of proliferation in CB. Conclusions: BC subtypes classified according to the St. Gallen clinicopathological definitions on CB show a high agreement with corresponding SSP results. The respective PPVs are also generally high. This means that clinicopathological subtyping on CB can be used for preoperative decision making in the vast majority of cases. However, for the Her2 negative subgroup of Luminal B subtype in CB the agreement with SSP is lower due to underestimation of proliferation in CB. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD06-05.