Predicting pathological complete response (pCR) to neoadjuvant trastuzumab in patients with breast cancer using HER2 mass spectrometry.

• DOI: 10.1200/jco.2018.36.15_suppl.e12643
• Publication Date: 2018-09-05T14:14:13Z
• Authors: Elisa Gasparini; Fabiola Cecchi; Roberto di Cicilia; Elisabetta Kuhn; Giuseppe Falco; Guglielmo Ferrari; Moira Foroni; Ione Tamagnini; Cristina Bassano; Yuan Tian; Stephen Charles Benz; Todd A. Hembrough; Alessandra Bisagni
• Keywords: Neoadjuvant Therapy

e12643 Background: Around 40% of HER2-positive (HER2+) breast cancer patients who receive trastuzumab-based neoadjuvant therapy (TNT) achieve pCR (the FDA-recommended outcome measure in this setting). The ability to predict which will respond TNT could support decisions regarding selection agents or combinations. We previously quantified tumor expression HER2 with mass spectrometry archived biopsies received adjuvant trastuzumab; levels > 2200 amol/ug protein were associated superior disease-free and overall survival. hypothesized that cutoff would a HER2+ population treated TNT. Methods: Formalin-fixed, paraffin-embedded from microdissected solubilized for proteomic profiling multiplexed spectrometry. Patients dichotomized using the pre-specified amol/ug. Relationships between pre-treatment following assessed Fisher’s exact test. Results: Of 65 evaluable patients, 18 achieved (overall rate 28%). In above (n = 30), was approximately 3 times higher than lower expressors 35) (43% vs. 14%; [odds ratio 4.47; [95% CI: 1.23-18.94], p 0.013). Among expressors, 86% did not pCR. HER3 co-expressed 29 patient tumors including 50% non-pCR samples. Conclusions: diagnosed as standard methods, quantitative identified subset low on Quantitative testing may be more useful assessment methods predicting response Multiplexed analysis co-expression potentially inform treatment dual pertuzumab.