Shi, Xuting

11063 Background: Dacetuzumab (SGN-40) is a humanized IgG1 monoclonal antibody that binds to CD40, mediates effector cell functions, and activates downstream apoptosis signaling pathways. Dacetuzumab has shown single-agent activity in relapsed/refractory DLBCL in phase I and phase II trials, with multiple objective responses and 1/3 of patients demonstrating tumor shrinkage, defined as a decrease in tumor volume (SPD) of at least 10%. We previously reported a 14-gene signature (ASH 2008 #1593) that was strongly associated with dacetuzumab sensitivity in DLBCL cell lines. Here, we report an initial evaluation of the gene signature as a classifier of patients likely to demonstrate tumor shrinkage after dacetuzumab therapy. Methods: The original 14 microarray probes were chosen for high correlation with in vitro dacetuzumab sensitivity (IC25) in 31 NHL cell line models. Matching qRT-PCR probes were developed and confirmed to correlate with the microarray probes in paired cell line samples. In this retrospective analysis, archived paraffin blocks from a 26 patient subset of the phase I and II trials, with a diagnosis of DLBCL and available tumor measurements, were assayed by qRT-PCR. Results: Overall, 42% of patients (11/26) exhibited decreased SPD of at least 10%. Of those who were marker +, 10 out of 13 (78%) had 10% or better decreases in SPD, whereas only 1 of 13 patients who were marker - demonstrated tumor shrinkage (8%). The overall accuracy for predicting tumor shrinkage was 85% (one-sided P=0.002, by permutation test). Among the 14 genes contributing to the multivariate signature, CD22 and VNN2 were the most strongly down-regulated in specimens from patients without at least a 10% decrease in SPD (P=0.14 and P=0.10, respectively), while IGF1R and CTSC were the most strongly up-regulated (P=0.05 and P=0.08, respectively). Conclusions: A 14-gene signature appears to predict tumor shrinkage in DLBCL patients receiving dacetuzumab in single-agent clinical trials (P=0.002). A larger clinical data set will be analyzed to further evaluate the correlation of this gene signature with objective clinical response rates.. [Table: see text]