Pitot, Henry C.

5053 Background: Genomic aberrations associated with resistance/response to AA/P are not known. In a prospective study we assessed whole-exome/RNA-seq based aberrations in CRPC metastatic biopsies for identifying molecular markers associated with primary resistance and response duration. Methods: Sequencing of metastatic biopsies was performed for analyzing molecular aberrations that predict primary resistance (defined as progression at 12-weeks of therapy (non-responders) using PSA, RECIST, bone scan criteria per PCWG2). Gene network analysis was performed in genes mutated more frequently in non-responders and in genes differentially expressed between non-responders and responders using a “risk ratio” (RR) of ≥2. Cox regression models with multiple gene network pathways were used for determining association with time to treatment change (TTTC). Results: Of 92 enrolled pts 82 had complete whole-exome, RNA-seq & 12-week outcome data available for analysis. At 12-weeks 33/82 had progressed. Using a RR of ≥2, 113 genes were more frequently mutated in non-responders & 292 in responders. In non-responders, gene network analysis revealed frequent mutations in Wnt/β-catenin pathway genes; frequent deletion of negative regulators of Wnt pathway ( DKK4, SFRP2, LRP6). Gene expression analyses revealed significantly reduced expression levels of Wnt/β-catenin pathway inhibitors and increased expression levels of cell cycle proliferation (CCP) genes in non-responders. Median study follow up was 32 months during which time 58/82 pts progressed and switched treatments. Median TTTC was 10.1 months (IQR:4.4-24.1). In multivariate analysis CCP scores of ≥50 predicted shorter TTTC (HR = 2.11, 95% CI: 1.17-3.80; p = 0.01). Conclusions: In metastases Wnt/β-catenin pathway activation is associated with primary AA/P resistance and increased CCP with acquired drug resistance. These findings offer molecular based predictive biomarkers in CRPC stage treatment. Clinical trial information: NCT#01953640.

3554 Background: There is considerable variability in the outcomes between second line (SL) trials in mCRC. The aim of this analysis is to compare the outcomes of patients (pts) with mCRC treated either on SAFL, with protocol defined SL treatment, or DSLT. Methods: Individual pt data was available on pts with mCRC enrolled in 1 of 10 trials (7 DSLT, 3 SAFL) in the ARCAD database. Regimens included FOLFIRI, FOLFOX, and irinotecan (IRI), since pts did not receive biologic agents in SL on SAFL. For pts on a SAFL, PFS and OS were defined as time from initiation of SL treatment to second progression (SP)/death and death, respectively. Descriptive statistics and multivariable Cox models were used to assess differences in PFS and OS. Results: 5,076 pts were included; 63% were male; median age was 62. See Table for treatment details. Pts treated on SAFL had shorter OS (0.7-1.5 months (mos>) shorter) and PFS (0.6-2.6 mos shorter), compared to those treated on DSLT. These findings were statistically significant and differences in OS did not attenuate after adjustment for age, gender, and prior treatment. PFS differences in FOLFOX became insignificant after multivariable adjustment. Conclusions: There are modest differences in both PFS and OS between pts with mCRC treated on SAFL and those on DSLT, suggesting differences in these pt populations. Caution is needed when applying these data to pts, as we were unable to control for potential confounders (ECOG PS, number and sites of metastases) at initiation of SL in SAFL, which may impact outcomes. [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]