Impact of the Prosigna (PAM50) assay on adjuvant clinical decision making in patients with early stage breast cancer: Results of a prospective multicenter public program.

e12062Background: Prosigna is a standardized test based on the PAM50 gene signature which provides information on intrinsic subtype and risk of recurrence (ROR) score predicting 10y recurrence probability (NanoString Technologies, Inc., Seattle, WA). We evaluated Prosigna’s impact on adjuvant treatment decision beyond immunohistochemistry (IHC) testing. Methods: 125 pre- and postmenopausal EBC patients with ER+, HER2-, pT1-T2 pN0/pN1mi were enrolled (12 centers; 8/2015-11/2016). FFPE specimens were centrally analyzed using Prosigna to classify patients according to the intrinsic tumor subtype and ROR score. The primary endpoint was the impact of the Prosigna test on adjuvant treatment decision. Results: 64% of tumors were classified by PAM50 as Lum A, 35% as Lum B, 0% Basal, 1% HER2-E. The intrinsic subtype concordance between immunohistochemistry (IHC) and Prosigna (n = 119) was 61.3%. In Lum B tumors by IHC the discordance rate was the highest (48% were reclassified as Lum A by Prosigna) as shown in the...