The study was terminated by the sponsor following unblinding of the Progression Free Survival endpoint.

The purpose of Part 1 of this study is to evaluate the safety and tolerability of dalantercept in combination with axitinib in patients with advanced renal cell carcinoma (RCC) to determine the recommended dose level of dalantercept in combination with axitinib for Part 2.

The purpose of Part 2 of this study is to determine whether treatment with dalantercept in combination with axitinib prolongs progression free survival (PFS) compared to axitinib alone in patients with advanced renal cell carcinoma (RCC).

In Part 1 of the study, groups of subjects received escalating doses of dalantercept; 0.6, 0.9 and 1.2 mg/kg in sequential groups. All subjects received concurrent axitinib 5 mg PO BID. A total of 29 subjects were enrolled i Part 1 of the study.

In Part 2, dalantercept at 0.9 mg/kg once every 3 weeks plus axitinib 5 mg PO BID was compared to placebo plus axitinib 5 mg PO BID. A total of 131 subjects were enrolled in Part 2 for a total of 160 in the study

Key Inclusion Criteria:

• Histologically confirmed, advanced, predominantly clear cell renal cell carcinoma (RCC).
• Part 1: Progression of disease following up to three lines of prior therapy, including at least one approved VEGF receptor tyrosine kinase inhibitor for RCC. Adjuvant therapy is permitted as one line of prior therapy.
• Part 2: Progression of disease following one VEGF pathway inhibitor for RCC (e.g. sunitinib, pazopanib, sorafenib, bevacizumab, tivozanib, or cabozantinib) inclusive of adjuvant therapy if there was documented disease progression during treatment. Patients may have received one additional line of an approved mTOR kinase inhibitor (e.g. everolimus, temsirolimus). Prior exposure to investigational and/or approved anticancer immune therapies is permitted.
• A minimum of 1 week since the last dose of prior therapy (a minimum of 4 weeks since anticancer immune therapy or bevacizumab +/- interferon).
• Measurable disease that is evaluable by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• Life expectancy of at least 12 weeks.
• Clinical laboratory values within acceptable ranges within 72 hours prior to study day 1.

Key Exclusion Criteria:

• Clinically significant organ/system disease unrelated to RCC that in the judgment of the investigator should preclude treatment with dalantercept or axitinib.
• Clinically significant cardiovascular risk.
• Known CNS metastases or leptomeningeal disease:

For Part 1, patients with CNS metastases treated with whole brain radiotherapy, gamma knife, and/or surgery who are considered stable by CNS imaging and are not being treated with corticosteroids 6 weeks prior to study day 1 may be enrolled.

For Part 2, patients with CNS metastases treated stereotactic radio-surgery (SRS), and/or surgery who are considered stable by CNS imaging for at least 2 months prior to enrollment and are not being treated with corticosteroids 6 weeks prior to study day 1 may be enrolled.

• Any active malignancy, other than RCC, for which chemotherapy or other anti-cancer therapy is indicated. Patients with adequately treated non-melanoma skin cancer, in situ cancer, or other cancer from which the subject has been disease-free for at least 3 years will be permitted.
• Any lesion invading or having encasement ≥ 180 degrees around the wall of a major blood vessel as assessed by computed tomography (CT) scan and/or magnetic resonance imaging (MRI).
• Radiotherapy within 2 weeks prior to study day 1.
• Lack of recovery from toxic effects of previous treatment for RCC ≤ grade 1 with the exception of alopecia, unless stabilized under adequate medical control.
• Patients undergoing renal dialysis.
• Major surgery within 4 weeks prior to study day 1 (patients must have recovered completely from any previous surgery prior to study day 1).
• Any active infection requiring antibiotic therapy within 2 weeks of study day 1.
• Anti-coagulation therapy. Aspirin, other anti-platelet agents, and low molecular weight heparin are permitted unless the investigator deems the patient is at a significant risk for bleeding.
• Current use or anticipated inability to avoid potent CYP3A4/5 inhibitors or inducers (please refer to the Inlyta® [axitinib] prescribing information) during participation in the study.
• Peripheral edema requiring medical intervention within 2 weeks prior to study day 1.
• Bleeding diathesis including clinically significant platelet disorders or active hemoptysis (defined as bright red blood of ≥ 1/2 teaspoon [2.5 mL] in any 24 hour period) within 6 months prior to study day 1. For clinically significant epistaxis within 4 weeks prior to study day 1, no risk of further bleeding must be clearly documented.
• Known history of hereditary hemorrhagic telangiectasia (HHT).
• Known active hepatitis B virus (HBV) or hepatitis C virus (HCV) infections or positive human immunodeficiency virus (HIV) antibody results. Patients with sustained virologic response to HCV treatment or immunity to HBV from prior infection without cirrhosis may be included.
• History of severe (defined as ≥ grade 3, using the National Cancer Institute Common Toxicity Criteria for Adverse Events, version 4.0 [NCI-CTCAE] v4 current active minor version) allergic or anaphylactic reaction or hypersensitivity to recombinant proteins or excipients (10 mM Tris buffered saline) in the investigational agent.
• Any prior treatment with dalantercept or any other agent targeting ALK1 pathway.
• Any prior treatment with axitinib.
• A morbidity (per the prescribing information) that would require starting a patient at a reduced dose of axitinib.
• Treatment with another investigational drug (with the exception of anticancer immune therapy) or device, or approved therapy for investigational use, within 5 times the half-life of the drug or within 3 weeks prior to study day 1 if the half life is not known.
• Pregnant or lactating female patients.