Abstract

Vascular endothelial growth factor (VEGF) plays a seminal role in neo-angiogenesis. VEGF is present on myeloma cells, and its receptors, VEGFR1 (Flt-1) and VEGFR2 (KDR) are detectable on the surface of neighboring myeloid and monocytic elements. Hence, VEGF is implicated in the pathogenesis of multiple myeloma (MM). Thalidomide, an important agent in the treatment of MM, among its many postulated mechanisms of actions also inhibits VEGF-mediated neo-angiogenesis. We set out to test the feasibility and explore the efficacy of combining an anti-VEGF agent with thalidomide. With the availability of the anti-VEGF antibody rhuMAB bevacizumab, a trial of bevacizumab 10 mg/kg given intravenously every 2 weeks alone (in thalidomide-exposed patients) versus a randomized comparison of bevacizumab +/− thalidomide 50–400 mg/day (in thalidomide naive patients) was initiated by the California Cancer Consortium. Twelve patients (median age:58 years; range:50–75) with initial stages of I (n:2), II (n:2) and III (n: 8), all with refractory MM have been enrolled. Patients received a median of 1 prior regimen (range:0–5). Six patients had failed an autologous stem cell transplant prior to enrollment. In patients who have received bevacizumab alone, grade 3 toxicities included fatigue and neutropenia (1), hypertension (1), and hyponatremia (1). In the group receiving bevacizumab and thalidomide, grade 3 lymphopenia was observed in 1 patient during cycle 3, and one patient was taken off study due to exacerbation of pre-exisiting (diet pill induced) pulmonary hypertension and was considered inevaluable. Median time to progression for the 6 patients treated with bevacizumab alone was 2 (range 1–4) months. Progression-free survival for the 5 evaluable patients treated with bevacizumab and thalidomide is 6 +, 7, 8 +, 10, and 30 + months, with 2 patients still on study and in response. Two of these patients did not progress but were taken off study (one for patient’s choice, and one due to the physician’s choice to pursue a stem cell transplant at 7.5 months, this patient is listed above as in response at 30 + months). Immunohistochemical staining (IHC) revealed 2 + to 4 + expression of VEGF on myeloma cells in 7 cases of the available 8 pre-treatment bone marrow samples. Weak staining (1+) of VEGFR1 was observed on the surface of myeloma cells in 5 cases. VEGFR2 expression was also observed on plasma cells by IHC (1+ to 2+) in 5 cases. Myeloma cells from a patient treated with bevacizumab alone for a duration of 4 months, and from a patient receiving bevacizumab and thalidomide for 7.5 months before going on to transplant, demonstrated the strongest staining intensity for VEGF. Due to slow accrual the study had been closed to accrual, although 2 patients continue on the bevacizumab and thalidomide arm. However, in light of our findings further testing of bevacizumab, preferably in combination with other active agents is warranted. Supported by NO1 CM 17101.

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