This exploratory, open label study will assess the the dose-effect relationship, efficacy and safety of RO5323441 in patients with metastatic treatment-refractory colorectal or ovarian cancer. Cohorts of patients will receive doses of intravenous RO5323441 in the range of 25mg to 3g every 1 or 2 weeks and will undergo serial dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) assessments. In the absence of disease progression and unacceptable toxicity, patients may continue to receive their maximum dose of RO5323441 for a core treatment phase of up to a total of 6 months. Treatment with RO5323441 can be extended at the investigator's discretion until disease progression or unacceptable toxicity occurs. Target sample size is <100.

Inclusion Criteria:

• adult patients, >/=19 years of age
• metastatic or unresectable colorectal or ovarian cancer refractory to, or unsuitable for standard therapy
• presence of tumor lesions suitable for DCE-MRI evaluation
• WHO performance status 0-1
• adequate bone marrow, liver and renal function

Exclusion Criteria:

• patient unsuitable for MRI scanning (e.g. metal implants, pacemaker, claustrophobia, hypersensitivity to DCE-MRI contrast material)
• brain metastases
• clinically significant ascites
• active bleeding, bleeding diathesis, oral anti-vitamin K medication (other than low dose coumarin) or history of coagulation disorders
• radiation therapy within 3 weeks, or anti-neoplastic therapy <30 days prior to first dose of study drug
• chronic therapy with systemic steroids or another immunosuppressive agent <2 weeks prior to first dose of study drug
• treated with bevacizumab in last regimen of systemic therapy