Bhatt, Rupal S.

There are no biomarkers predictive of resistance to docetaxel or cabazitaxel validated for patients with metastatic castration-resistant prostate cancer (mCRPC). We assessed the association between ABCB1 amplification and primary resistance to docetaxel or cabazitaxel for patients with mCRPC, using circulating cell-free DNA (cfDNA). Patients with ≥1 plasma sample drawn within 12 months before starting docetaxel (cohort A) or cabazitaxel (cohort B) for mCRPC were identified from the Dana–Farber Cancer Institute IRB approved database. Sparse whole genome sequencing was performed on the selected cfDNA samples and tumor fractions were estimated using the computational tool ichorCNA. We evaluated the association between ABCB1 amplification or other copy number alterations and primary resistance to docetaxel or cabazitaxel. Of the selected 176 patients, 45 samples in cohort A and 21 samples in cohort B had sufficient tumor content. No significant association was found between ABCB1 amplification and primary resistance to docetaxel (p = 0.58; odds ratio (OR) = 1.49) or cabazitaxel (p = 0.97; OR = 1.06). No significant association was found between exploratory biomarkers and primary resistance to docetaxel or cabazitaxel. In this study, ABCB1 amplification did not predict primary resistance to docetaxel or cabazitaxel for mCRPC. Future studies including ABCB1 amplification in a suite of putative biomarkers and a larger cohort may aid in drawing definitive conclusions.

8010 Background: In patients (pts) with metastatic melanoma (MM), tumor angiogenesis has been associated with tumor progression and survival (Ugurel et al, JCO 19:577). Microtubule and cyclooxygenase (COX)-2 inhibitors, both alone and in combination, have been shown to have inhibitory effects on endothelial cells and tumor angiogenesis both in vitro and in vivo (Merchan et al, Int J Ca 113:490. Jones et al, Nat Med 5:1418). We tested the safety and efficacy of a regimen involving low dose, continuous infusion (CIV) paclitaxel and oral celecoxib in pts with MM. Methods: Pts received paclitaxel 10mg/m2 for 96 hours weekly by CIV and Celecoxib 400 mg po/bid. Systemic tumor response was assessed at 6 wk intervals (1 cycle (C)). Pts without unacceptable toxicity or clinically significant disease progression (PD) received additional cycles. Pts exhibiting PD after C 2 relative to end of C 1 were removed from study. Pts on anticoagulants, with recent MI or untreated brain metastases were ineligible. Results: 20 pts (12 M/ 8 F), median age 55 (range 44–65), ECOG PS 0/1/2 (5/13/2), M1a/M1b/M1c: 1/1/18 (90%), and prior systemic therapy regimens 0/1/2/3+: 1/7/5/7 were enrolled in the protocol. Sites of systemic disease included: lung (13 pts), LN (14), soft tissue (13), liver (9), bone (4), brain (6), other (11). 3 pts came of study prior to treatment with rapid disease progression. Treatment related grade 3–4 toxicities included line related (LR) bacteremia (3 pts), LR DVT (3 pts), LR PE (3). There were no grade 3–4 toxicities attributed to paclitaxel or celecoxib. No pt exhibited a major tumor response; 6/20 (30%) pts had stable disease for 17, 18, 18, 18+, 30+, 60 wks. Median TTP was 6 wks (range 3- 60); median overall survival was 6 months (range 1–29). Conclusions: Low-dose, CIV paclitaxel and oral celecoxib leads to disease stabilization in a significant portion of previously treated pts with MM. This suggests a role for combination anti-angiogenic therapy in MM. The incidence of LR toxicities indicates that alternative microtubule inhibitors, such as oral taxanes, should be considered in combination with COX-2 inhibitors for future studies. Results of biomarker studies will be presented at the meeting. Supported by Pfizer Inc. and NIH R21 CA097730. [Table: see text]

174 Background: Docetaxel (D) and cabazitaxel (C) are standard chemotherapies for mCRPC. A reliable biomarker predictive of resistance to D or C is yet to be identified. We aimed to assess the association between genetic amplification of the multidrug resistance transporter ABCB1 (ABCB1 amp) and primary resistance (RES) to D or C for mCRPC, using cfDNA. Methods: A cohort (A) of 136 patients (pts) with at least 1 plasma sample drawn and stored within 1 year prior to starting D for mCRPC (2002-2014) and a cohort (B) of 42 pts with at least 1 plasma sample from within 1 year prior to starting C for mCRPC (2010-2016) were identified from the Dana-Farber Cancer Institute IRB approved database. Whole genome sequencing (WGS) at 0.1x coverage, termed ultra-low pass WGS (ULP-WGS), was performed on cfDNA extracted from the selected samples (1000μL/subject) and sequencing data were analyzed using a tool called ichorCNA to identify cases with sufficient tumor DNA content (>7%) for accurate detection of copy number alterations (CNAs) including ABCB1 amp. Primary objective was the association between ABCB1 amp and RES to D or C. RES was defined as lack of response (no PSA50 decline or radiologic response per RECIST criteria 1.1, within 4 months from treatment start). Odds ratio (OR) was used to compare odds of RES to D or C for pts with ABCB1 amp and P-values were calculated by Fisher’s exact test. Results: Of the selected 178 pts, 66 had tumor fraction >7%: 45 pts in cohort A and 21 in cohort B. No significant association was noted between ABCB1 amp and RES to D (P=0.7123; OR=1.600) or C (P=1.000; OR=1.0606). RES was observed in 26 pts (57.8%) of cohort A and 18 (85.7%) of cohort B. ABCB1 amp was found in 9 pts (20%; 95% CI, 9.6-34.6) in group A and 6 of them (66%) had RES to D. ABCB1 amp rate among D-resistant men was 23.1% (95% CI, 9.0-43.7). In group B, 2 pts (9.5%; 95% CI, 1.2-30.4) had ABCB1 amp and both of them had RES to C. ABCB1 rate among C-resistant pts was 11.1% (95% CI, 1.4-34.7). Conclusions: In this study, ABCB1 amp using cfDNA did not show statistically significant correlation with RES to D or C for pts with mCRPC. Future studies including ABCB1 amp in a suite of putative biomarkers and larger sample size may aid drawing definitive conclusions.

Abstract Purpose: High-dose aldesleukin (HD IL2) received FDA approval for the treatment of metastatic renal cell carcinoma (MRCC) in 1992, producing a 14% objective response rate (ORR) and durable remissions. Retrospective studies suggested that clinical and pathologic features could predict for benefit. The Cytokine Working Group conducted this prospective trial to validate proposed predictive markers of response to HD IL2. Experimental Design: Standard HD IL2 was administered to prospectively evaluate whether the ORR of patients with mRCC with “good” predictive pathologic features based on an “integrated selection” model [ISM (e.g., clear-cell histology subclassification and carbonic anhydrase-9 (CA-9) IHC staining] was significantly higher than the ORR of a historical, unselected population. Archived tumor was collected for pathologic analysis including tumor programmed death-ligand 1 (PD-L1) expression. Results: One hundred and twenty eligible patients were enrolled between June 11 and September 7; 70% were Memorial Sloan Kettering Cancer Center (New York, NY) intermediate risk, 96% had clear cell RCC, and 99% had prior nephrectomy. The independently assessed ORR was 25% (30/120, 95% CI, 17.5%–33.7%, P = 0.0014; 3 complete responses, 27 partial responses) and was higher than a historical ORR. Thirteen patients (11%) remained progression free at 3 years and the median overall survival was 42.8 months. ORR was not statistically different by ISM classification (“good-risk” 23% vs. “poor-risk” 30%; P = 0.39). ORR was positively associated with tumor PD-L1 expression (P = 0.01) by IHC. Conclusions: In this prospective, biomarker validation study, HD IL2 produced durable remissions and prolonged survival in both “good” and “poor-risk” patients. The proposed ISM was unable to improve the selection criteria. Novel markers (e.g., tumor PD L1 expression) appeared useful, but require independent validation. Clin Cancer Res; 21(3); 561–8. ©2014 AACR.