Vandetanib in metastatic hereditary medullary thyroid cancer: Follow-up results of an open-label phase II trial

6018 Background: Medullary thyroid cancer (MTC) is the most common cause of death in patients with hereditary syndromes caused by activating mutations in the RET protooncogene. RET activation is the initial oncogenic event, with the activity of other receptor tyrosine kinases, including VEGFR and EGFR, likely to contribute to tumor growth and metastasis. Vandetanib (ZD6474) is a once- daily oral agent that selectively targets RET, VEGFR and EGFR tyrosine kinases. Methods: Eligible patients had unresectable, measurable, locally advanced or metastatic hereditary MTC and a RET germline mutation. Patients received vandetanib 300 mg/day until disease progression or any other withdrawal criteria. The primary objective was to assess the objective tumor response (RECIST every 3 months). Secondary assessments included disease control rate, biochemical response (determined by decrements in plasma levels of calcitonin, a tumor marker for MTC) and safety and tolerability. Results: Thirty patients (21 female; median age 50 years) received initial treatment with vandetanib 300 mg. At data cut-off (20 Nov 2006), the median duration of treatment was 172 days. Based on site investigator assessments, 20% (6/30) of patients experienced a partial response (duration of response 59–260 days) and another 30% (9/30) of patients experienced stable disease =24 weeks, yielding a disease control rate of 50% (15/30). Centralized independent confirmation of response is planned. In 19 patients, plasma calcitonin levels showed a =50% decrease from baseline that was maintained for at least 6 weeks. Adverse events (AEs) occurring in >50% of patients were rash (73%), diarrhea (67%), fatigue (57%) and nausea (53%). Most AEs were grade 1 or 2; grade 3 AEs included asymptomatic QTc prolongation (n=5), rash and diarrhea (both n=3), all of which were manageable. Conclusions: Vandetanib has demonstrated clinical activity in this phase II study in metastatic hereditary MTC, and the safety profile is generally consistent with previous vandetanib monotherapy studies. Accrual is now complete (30 patients), and an updated analysis will be performed in April 2007. An international, randomized, placebo-controlled phase II trial of vandetanib in MTC is now recruiting patients. # No significant financial relationships to disclose.