Oh, Cindy

4147 Background: Retrospective studies of phosphorylated STAT3 (pSTAT3, a regulator of gene expression) in cancer-lineage cells have suggested it is a biomarker of poor prognosis. We analyzed data from 3 phase 3 RCTs (BRIGHTER [T1; NCT02178956], CO.23 [T2; NCT01830621], CanStem111P [T3; NCT02993731]) to evaluate the prognostic impact of pSTAT3 on OS in GI cancer patients (pts). Methods: pSTAT3 was evaluated in archival tumor tissue from pts with gastric or gastroesophageal junction adenocarcinoma (T1), colorectal cancer (T2), or pancreatic cancer (T3) who received standard of care in the control arms (CTL) of their respective trials. pSTAT3 positive (+) or negative (−) status was determined by detecting pSTAT3 in both tumor and tumor microenvironment (TME) cells in a laboratory-developed immunohistochemistry (IHC) assay (T1; T2), later developed into the investigational pSTAT3 IHC D3A7 assay (Agilent Technologies, Inc.) (T3). The positivity cutoff requires a sample have both a TME score of 2 and ≥5% of tumor cells staining positively for pSTAT3. Pre-analytical variables (eg, specimen collection, handling, and processing), tumor indication, and slight differences in the assays used for each study may contribute to relative differences in evaluable rates between studies. In an exploratory analysis, OS was compared in pSTAT3+ vs pSTAT3− pts via an unstratified log-rank test. Results: In each study, intent-to-treat pts with evaluable pSTAT3 results were considered pSTAT3-evaluable. This abstract includes pSTAT3-evaluable pts randomized to the CTL arms (T1: n/N=248/357, 69.5%; T2: n/N=110/144, 76.4%; T3: n/N=243/569, 42.7%). Baseline characteristics are presented in the table. Median (m) OS was shorter in pts with pSTAT3+ tumors across all studies (T1 hazard ratio [HR]=1.32 [95% confidence interval (CI): 1.00, 1.74]; T2 HR=2.40 [1.50, 3.83]; T3 HR=1.08 [0.77, 1.50]). Conclusions: In pSTAT3-evaluable populations from 3 RCTs across GI cancers, CTL pts with pSTAT3+ (vs pSTAT3−) tumors had shorter mOS. These results suggest that pSTAT3 positivity may be a biomarker of poor clinical outcome. Clinical trial information: NCT02178956; NCT01830621; NCT02993731. [Table: see text]

4106 Background: Cancer stem cells are fundamentally important for resistance to therapy, recurrence and metastasis. Napabucasin is a first-in-class cancer stemness inhibitor in development identified by its ability to inhibit STAT3-driven gene transcription and spherogenesis of cancer stem cells (Li et al, PNAS 112(6):1839, 2015). Preclinical studies suggest that napabucasin sensitizes heterogeneous cancer cells to chemotherapy and targeted agents. Methods: A phase Ib/II multi-center study in mPDAC pts was performed to confirm the RP2D, PK profile and evidence of anticancer activity of napabucasin in combination with nabPTX and Gem. Pts received napabucasin 240 mg BID with weekly nabPTX 125 mg/m2 and gem 1000 mg/m2for 3 out of every 4 weeks until disease progression (PD) or other discontinuation criterion. Results: Of 71 intent to treat (ITT) pts enrolled, 49 (69%) were treatment-naïve and 22 (31%) received neoadjuvant treatment. There were no significant PK interactions, dose-limiting or unexpected toxicities. Most common adverse events (AEs) included grade 1 diarrhea/cramping, nausea and fatigue with grade 3 AEs noted in 12 pts: fatigue (8), electrolyte imbalance (2), diarrhea (1), dehydration (1), nausea (1) and weight loss (1). Among pts who received RECIST evaluation (60), disease control (DCR; CR+PR+SD) was observed in 55 (92%), with 1 CR (2%) and 26 PR (43%) (31 - 78% regression). Of 11 pts with non-evaluable disease, treatment stopped due to compliance (4), consent withdrawal (3), clinical PD (1), toxicity (1), insurance (1) and death (1). Among 71 ITT pts, DCR was observed in 55 (77%), with 1 CR (1.4%) and 26 PR (37%). Maturing median progression free survival and overall survival (OS) in ITT pts is >7.1 and >10.4 m, respectively. Conclusions: This study showed that napabucasin can be combined with nabPTX and gem, with encouraging signs of efficacy in mPDAC now being confirmed in a phase 3 study. Clinical trial information: NCT02231723. [Table: see text]