Abstract
570 Background: H is a humanised monoclonal antibody directed at HER2. The extracellular domain (ECD) of the HER2 protein may be shed into the serum and is detectable using ELISA. A correlation has previously been suggested between baseline shed ECD and response. This relationship as well as the effect of trastuzumab [Herceptin (H)] and chemotherapy on ECD levels are investigated. Methods: Data are presented from 4 phase II/III clinical trials: Study BO15935: q3w H + paclitaxel (P) in MBC (N=30 patients analysed for ECD) Study M77001: q3w docetaxel (D) +/- qw H in MBC (N=135) Study WO16229: q3w H alone in MBC (N=98) Study BO15899: qw Gemcitabine/Cisplatin (GC) +/- H in NSCLC (N=103) ECD sampling frequency varied between studies from every cycle to every third cycle. Results: No clear relationship was found between baseline ECD levels and best clinical response. After the start of therapy, ECD levels fell irrespective of the agent(s) received. Cytotoxics +/- H resulted in rapid large reductions in ECD followed by a relative plateau (eg study M77001: median ECD declined from baseline of 30.2 ng/ml (n=136) to 9.8ng/ml (n=97) at cycle 6 (week 16)). However, H monotherapy led to a slower, more steady reduction over the duration of treatment (eg study WO16229: declined from baseline of 31.4 ng/ml (n=98) to 8.7 ng/ml (n=2) at cycle 24 (week 70)). There was no obvious difference in the course or the extent of decline when analysed by best response. Additional longitudinal analyses will be presented. Conclusions: In these studies including a total of 366 patients, there was no obvious relationship between baseline ECD levels and response. In all cases ECD levels dropped with antiproliferative therapy. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Roche Genentech; Lilly; Roche Roche AstraZeneca Hoffmann-LaRoche
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