Abstract 735: HER2 protein quantification in multiple cancer indications identifies candidates for HER2 targeted therapies (2017)

Abstract Background: Anti-HER2 therapy in cancer indications other than breast and gastric cancers is the subject of ongoing clinical trials. We previously used mass spectrometry to identify HER2 protein expression level cutoffs that correlate with standard measures of HER2 positivity (740 and 750 amol/µg in breast and gastric cancers, respectively). These studies also demonstrated that trastuzumab-treated patients whose tumors express high levels of HER2 (≥ 2200 and ≥ 1825 amol/µg in breast and gastric cancers, respectively) survived much longer than patients with lower HER2 levels. We hypothesized that targeted proteomics would reveal high HER2 levels in indications other than breast and gastric cancers, thus identifying patients likely to benefit from anti-HER2 therapy. Methods: We summarized results from samples processed in our CAP/CLIA-certified laboratory. Tumor areas from FFPE tissue blocks (N=3828) representing multiple cancer indications were marked by a pathologist, microdissected, and solubilized to tryptic peptides. In each liquefied tumor sample, HER2 and other protein targets were quantified with mass spectrometry-based proteomic analysis. Results: HER2 superexpression (&gt; 2200 amol/µg) was found in 0.64% (12/1891) of patients with non-breast, non-gastroesophageal cancers. Among indications with &gt; 50 patients tested, the highest rates of HER2 superexpression were in gynecological cancers (3/124; 2.4%) and bladder cancer (1/51; 2.0%). Treatment and outcome data are largely unavailable, but we are aware of 3 anecdotes: In a 74-year-old male with invasive adenocarcinoma of the gallbladder who had disease progression on gemcitabine + cisplatin, proteomic testing found high HER2 protein expression (3105 amol/µg). The patient responded to trastuzumab + FOLFIRI for 5 months. In a uterine cancer patient whose HER2 status was equivocal by genomic analysis, proteomics found high HER2 expression (4995 amol/µg). Proteomics also revealed the absence of a resistance marker for taxane (TUBB3) and high levels of the response marker for antifolate agents (FRalpha = 10500 amol/µg). The patient responded to trastuzumab + taxol for 9 months before developing resistance and responding to trastuzumab + antifolate. Lastly, a cervical cancer patient whose disease had progressed on chemotherapy showed HER2 superexpression (11322 amol/µg). She was treated with anti-HER2 combinations for &gt; 12 months. Conclusions: Patients with high HER2 protein expression as measured by targeted mass spectrometry in multiple cancer types have benefitted from anti-HER2 therapy. Only small numbers of patients with non-breast, non-gastric tumors have HER2 protein levels indicative of survival benefit from anti-HER2 therapy. However, multiplexed targeted proteomics offers simultaneous, precise quantification of other biomarkers (eg, ERCC1, TUBB3, FRalpha) to guide therapy selection for multiple cancer types. Citation Format: Shankar Sellappan, Sarit Schwartz, Ellen Wertheimer, Fabiola Cecchi, Steven W. Mamus, Daniel VT Catenacci, Todd Hembrough. HER2 protein quantification in multiple cancer indications identifies candidates for HER2 targeted therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 735. doi:10.1158/1538-7445.AM2017-735