Phase I/II Trial of Vandetanib and Bortezomib in Adults with Locally Advanced or Metastatic Medullary Thyroid Cancer

LESSONS LEARNED. Vandetanib at a dose of 300 mg orally every day plus bortezomib 1.3 mg/m(2) intravenously on days 1, 4, 8, and 11 could be administered safely. Assessing outcomes in 17 patients with medullary thyroid cancer, investigators considered the combination to be more difficult to administer than single‐agent vandetanib and that achieving better outcomes was unlikely. Consequently, a planned phase II study was terminated early. BACKGROUND. The proto‐oncogene RET (REarranged during Transfection) has a critical role in the pathogenesis of medullary thyroid cancer (MTC). Vandetanib (V), a multitargeted tyrosine kinase inhibitor approved for the treatment of MTC, is thought to inhibit RET in MTC. Supported by preclinical studies demonstrating that bortezomib (B) administration lowered RET mRNA and protein levels, we conducted a phase I study in advanced solid tumors of vandetanib in combination with bortezomib. The goal was to establish an RP2D (recommended phase II dose) for the combination of vandetanib plus bortezomib, a regimen envisioned as a dual strategy for targeting RET in MTC. METHODS. Patients with advanced solid tumors were treated with escalating doses of bortezomib or vandetanib to assess the safety and tolerability of daily oral vandetanib and intravenous (IV) bortezomib administered on days 1, 4, 8, and 11 of a 28‐day cycle. Intrapatient dose escalation was allowed. RESULTS. Twenty‐two patients were enrolled and received escalating mg/m(2) bortezomib and mg vandetanib (number of patients) at initial doses of 1 and 100 (3), 1.3 and 100 (6), 1.3 and 200 (6), and 1.3 and 300 (7), respectively. Patients received a median of four cycles of bortezomib/vandetanib (range: 1–10), with 13 patients escalating to 1.3/200 and 10 to 1.3/300. G3 toxicities occurring in more than one patient included hypertension (24%), fatigue (19%), thrombocytopenia (10%), diarrhea (10%), and arthralgia (10%). There were no drug‐related G4/5 toxicities. There was one dose‐limiting toxicity, G3 thrombocytopenia, at bortezomib/vandetanib doses of 1.3/200 in cycle 2 that resolved without intervention. Four patients with a diagnosis of MTC (27%) had a partial response (PR). CONCLUSION. The MTD of the combination was established as bortezomib, 1.3 mg/m(2) IV days 1, 4, 8, and 11 with vandetanib 300 mg p.o. daily. RECIST responses were observed in patients with a diagnosis of MTC.