e15095 Background: Cabazitaxel is a semi-synthetic novel taxane with activity in docetaxel refractory prostate cancer. We sought to determine the response rate of cabazitaxel in patients with advanced gastroesophageal adenocarcinoma that had progressed after at least 1 prior therapy for metastatic disease. Methods: This open label single arm phase II study followed a Simon two-stage design. The study was designed to differentiate between a 10% level of activity and a 30% level of activity and was to be terminated if the response rate was unlikely to be > 10%. Eligibility criteria included patients with gastroesophageal cancer with measurable disease after at least 1 prior regimen for metastatic disease. ECOG PS 0-2; ANC > 1,500/µL, AST/ALT ≤ 3x ULN, total bili ≤ ULN. Pts initially received cabazitaxel 25 mg/m2 IV every 21 days but after 9 patients were entered, the dose was reduced to 20 mg/m2due to toxicity. Results: The data safety monitoring board (DSMB) reviewed data after 13 pts were entered. Pt characteristics included 11 men, 2 women; median age, 70 yrs [range, 55-80]. Nine pts had ≥ 2 prior regimens. Ten pts had previous treatment with a taxane. Of 13 pts, no objective antitumor responses were observed and all 13 developed evidence of disease progression. A median of 2 cycles were given, up to a maximum of 6 cycles in 2 pts. The PFS rate at 3 months was 15%. The DSMB considered cabazitaxel ineffective and terminated the study. The probability of erroneously concluding the treatment was active (p ≥ 0.3) was < 0.0419. Grade 3 or 4 adverse events occurred in 6 pts (46.1%), in which neutropenia (n=4) and pneumonia (n=1) were grade 4. Grade 3 toxicities included ANC (n=1), anemia (n=2), nausea (n=2), weakness (n=2), diarrhea (n=1), pleural effusion (n=1), typhilitis (n=1), vomiting (n=1). Conclusions: Cabazitaxel monotherapy demonstrated no antitumor efficacy in previously treated gastroesophageal cancer. Clinical trial information: NCT01365130.