Abstract P6-08-22: Functional subtyping with BluePrint 80-gene profile identifies two distinct triple positive subtypes with and without trastuzumab/chemo-sensitivity: Implications for treatment from the NBRST registry

Background Classification by molecular subtype can aid in the selection of therapy for patients with breast cancer. However at present, the methodology for molecular subtyping is not standardized and the methodology and interpretation of results vary between different laboratories. Subtype is being assigned using conventional immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) (conventional subtype) or molecularly using gene expression profiling. The aim of the current prospective NBRST study is to compare chemosensitivity as defined by pathological Complete Response (pCR), or endocrine sensitivity as defined by partial response (PR) using the 80-gene BluePrint functional subtype profile vs. conventional IHC/FISH subtyping. Methods MINDACT is an international, prospective, randomized, phase III trial investigating the clinical utility of MammaPrint in selecting patients with early BC for adjuvant chemotherapy (CT), which enrolled 6,694 patients. Molecular subtyping data were obtained by MammaPrint and BluePrint (Agendia, Amsterdam, the Netherlands) on frozen samples (n=6,694) classifying patients in the following subtypes: Luminal A (Luminal-type/MammaPrint Low Risk); Luminal B (Luminal-type/MammaPrint High Risk); HER2-type; and Basal-type. ER, PgR, HER2 and Ki67 protein status were centrally assessed on FFPE blocks by IHC and/or FISH in the European Institute of Oncology, Milan, Italy (n=5,740; 86%). Patients were also classified according to the St. 2013 Gallen recommendations [Goldhirsch et al. 2013], which recognizes an additional category (Luminal B-like HER2+). Results Ki67 is often used as biomarker to distinguish Luminal A from Luminal B subgroups. The concordance between MammaPrint and centrally assessed Ki67 in Luminal-type patients is 60%, with a κ score of 0.26 (95% CI 0.24–0.28) indicating that Ki67 and MammaPrint cannot reliably substitute for each other. When using a cut-point of 20% instead of 14% the concordance increased to 78%, with a κ score of 0.44 (95% CI 0.41–0.47). There is a relatively large group of clinical HER2+ cases that are BluePrint Luminal-type (208 out of 541; 38%) indicating that tumor expression of the Luminal profile is dominant compared with expression of the HER2 profile. These patients have high IHC ER results and all except for 1 fall into the group that St Gallen separately defines as Luminal B-like HER2-positive. These patients may have lower response to trastuzumab [von Minckwitz et al. JCO 2012]. 98 out of 622 BluePrint Basal-type patients are clinical Luminal HER2-. 2/3 of these patients have low centrally assessed IHC PR expression and 1/3 have low centrally assessed ER expression (≥1% and Conclusions Molecular subtyping using BluePrint and MammaPrint leads to a reclassification of 22% (113/515) of tumors. The re-classification of patients leading to re-assignment to more responsive vs. less responsive groups is most prominent in classically assessed triple positive patients where 46% of patients are re-assigned to the less responsive BP Luminal-type group (pCR rate of 7%) vs. 46% of patients assigned to the responsive BP HER2-type group (pCR rate of 49%). These findings confirm the more accurate identification of molecular subgroups for treatment decision by BluePrint functional subtype classifier which may therefore serve as a better guide for neo-adjuvant treatment than standard, local IHC/FISH assay. Citation Format: Pat Whitworth, Jennifer Beatty, Paul Baron, Paul Richards, James Pellicane, Angela Mislowsky, Charles Nash, Laura Lee, Mary Murray, Femke de Snoo, Lisette Stork-Sloots, Sarah Untch, Mark Gittleman, Stephanie Akbari, Peter Beitsch. Functional subtyping with BluePrint 80-gene profile identifies two distinct triple positive subtypes with and without trastuzumab/chemo-sensitivity: Implications for treatment from the NBRST registry [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 P6-08-22.