Jonker, Derek J.

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]

4090 Background: EGFR mAbs have become incorporated into clinical practice for the management of mCRC over the last decade. KRAS and NRAS mutations are used as predictive biomarkers and BRAF V600E mutations are associated with an adverse prognosis. The observed TE within biomarker subpopulations has varied between studies. Methods: IPD from randomized trials with head-to-head comparison between EGFR mAb versus no EGFR mAb (chemotherapy alone or BSC) in mCRC, across all lines of therapy (first, second and later), were pooled. Biomarker subpopulations are defined in the table. Overall survival (OS) and progression-free survival (PFS) were compared between groups by Cox model, stratified by studies and adjusted by age, gender, and performance status. TEs were estimated by adjusted hazard ratio (HRadj) and 95% confidence interval (CI). Within each biomarker subgroup, EGFR mAb efficacy was explored according to multiple exploratory factors, including line of therapy, type of backbone chemo, gender, sidedness and site of metastasis. Interaction tests were performed. P-values < 0.01 were considered statistically significant to account for multiple comparisons. Results: 5729 pts from 8 studies with data available for ≥ 1 biomarker were analysed. PFS benefits (median 9.2 mos in EGFR mAbs, 8.0 mos in no EGFR mAbs) were confirmed in triple-WT pts, but not for OS (refer to table). No OS/PFS benefits were observed for pts with any of the MT tumors. Exploratory analyses showed a potential detrimental TE of EGFR mAbs in KRAS MT mCRC with liver metastasis (OS: HRadj 1.22, p = .003, pinteraction .0056; PFS: HRadj 1.24, p = .0009, pinteraction .0008). These results were confirmed within the subgroup of pts with all 3 biomarkers available. Conclusions: This is the largest IPD analysis to explore the predictive value of RAS/BRAF biomarkers in mCRC. Our findings demonstrate that there is no evidence of efficacy of EGFR mAbs in KRAS, BRAF and/or NRAS MT mCRC. EGFR mAbs might have a detrimental effect in KRAS MT mCRC with liver metastases. [Table: see text]

3529 Background: Cancer stem cells are considered to be fundamentally important for resistance, 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). Preclinically, napabucasin sensitizes cancer cells to chemotherapy and targeted agents. Methods: A phase Ib/II multi-center study in mCRC pts was done to confirm the RP2D and signs of anti-cancer activity of napabucasin in combination with FOLFIRI +/- Bev. Pts received napabucasin 240 mg PO BID with bi-weekly FOLFIRI IV +/- Bev 5 mg/kg until disease progression or other discontinuation criterion. Results: 82 pretreated mCRC pts were enrolled (ITT); including 32 (39%) previously treated with FOLFIRI +/- bev. Of the 82 pts, 48 received FOLFIRI and 34 FOLFIRI plus bev in combination with napabucasin. There was no dose-limiting or unexpected toxicity or significant PK interactions. Most common adverse events (AEs) included grade 1/2 diarrhea, cramping, nausea, vomiting, fatigue and anorexia with grade 4 diarrhea in 1 pt and 27 pts with grade 3 AEs including: diarrhea (15), fatigue (5), dehydration (1), electrolyte imbalance (4), abdominal pain (1), vomiting (1) and weight loss (1), which resolved with dose reduction and supportive care. Disease control (CR+PR+SD) was observed in 55 of 66 pts who received RECIST evaluation (83%), with 1 CR (1.5%), 13 PR (20%) (33-100% regression) and 27 SD with tumor regression (41%). Conclusions: This phase Ib/II study confirmed that napabucasin can be safely combined with FOLFIRI +/- bev, and shows encouraging signs of efficacy in pretreated mCRC pts, including pts previously treated with FOLFIRI +/- bev. Clinical trial information: NCT02024607. [Table: see text]

593 Background: Cancer stem cells or stemness-high cancer cells are considered to be fundamentally important for resistance to therapy, recurrence and metastasis. Napabucasin, a first-in-class cancer stemness inhibitor in clinical development, suppresses cancer stemness by targeting Stat3-driven gene transcription. Preclinical studies suggest that napabucasin sensitizes heterogeneous cancer cells to chemotherapeutics and targeted agents. Methods: This study was performed to assess signs of anti-tumor activity of napabucasin in combination with FOLFIRI +/- Bev in CRC pts. Napabucasin was administered at 240 mg BID. FOLFIRI (5-FU 400 mg/m2 bolus with 2400 mg/m2, irinotecan 180 mg/m2, and leucovorin 400 mg/m2 infusion) +/- Bev 5 mg/kg was administered biweekly until disease progression or other discontinuation criterion. pSTAT3 status of archival tumor tissue was assayed by immunohistochemistry using the H-score with pSTAT3highdefined as ≥ 5% pSTAT3+ cancer cells and tumor stroma staining at ≥ 2+ intensity. Results: 63 CRC pts with an average of >2 prior therapy lines were enrolled. No pharmacokinetic interactions or dose-limiting toxicity was observed. Most common adverse events (AEs) included grade 1/2 diarrhea, nausea, vomiting and fatigue. 25 pts had grade 3 AEs, including diarrhea (14), fatigue (4), dehydration (2), electrolyte imbalance (4), nausea (1) and weight loss (1) resolved with dose reduction and supportive care. Among 63 pts enrolled who received RECIST evaluation, disease control (CR+PR+SD) was observed in 49 pts (86%) with an overall response (CR+PR) of 28% with 1 pt achieving CR. Clinical trial information: NCT02024607. Conclusions: This phase Ib/II study suggests napabucasin may sensitize chemorefractory CRC to FOLFIRI +/- Bev. Encouraging signs of synergistic activity between napabucasin and FOLFIRI was observed in CRC pts regardless of pSTAT3 status.[Table: see text]

569 Background: BBI-608 is an oral first-in-class cancer stemness inhibitor that blocks STAT3-mediated transcription of cancer stemness genes. Potent anti-CSC activity was observed in vitro and in vivo,in mono and combination therapy. In phase I studies, BBI-608 was generally well tolerated with encouraging signs of anti-tumor activity. Methods: A phase Ib open label, multi-center study in pts with advanced CRC was undertaken to confirm the RP2D of BBI-608 in combination with FOLFIRI with or without BEV. BBI-608 was administered at 240 mg BID in combination with FOLFIRI (5-FU 400 mg/m2 bolus with 2400 mg/m2, irinotecan 180 mg/m2, and leucovorin 400 mg/m2infusion) with or without BEV 5 mg/kg, administered bi-weekly until progression of disease, unacceptable toxicity, or other discontinuation criterion was met. Results: 18 heavily pretreated pts with an average of > 3 prior lines of therapy of which 10 pts (56%) previously progressed on FOLFIRI were enrolled. Of the 17 pts evaluable for response, 8 pts received FOLFIRI and 9 pts received FOLFIRI with BEV in combination with BBI-608. Most common adverse events included grade 1 and 2 diarrhea, abdominal pain, nausea, vomiting and anorexia. No dose limiting toxicity or new adverse events were seen, and the safety profile was similar to that of each regimen as monotherapy. Grade 3 events related to protocol therapy included diarrhea occurring in 3 pts, fatigue in 2 pts and dehydration in 1 pt. All events resolved after dose reduction and/or start of anti-diarrheal medications. No significant pharmacokinetic interactions were observed. Disease control (PR+SD) was observed in 16 of 17 evaluable pts (94%) with 2 PR (per RECIST 1.1 criteria: 44% and 33% regression) and 14 SD (of which 13 (93%) had tumor regression < 25%). In the evaluable pts, median progression free survival was 5.54 months. Of 17 pts, 7 (41%) had prolonged SD of > 6 months. Conclusions: This phase Ib study confirmed that BBI-608 at 240 mg bid can be safely combined with FOLFIRI with and without BEV, and shows encouraging anti-tumor activity in heavily pretreated CRC pts, even in pts with prior progression on FOLFIRI-based therapy. Clinical trial information: NCT02024607.