 The purpose of this study is to investigate the safety and efficacy of three different regimens of PAN 20 mg TIW, 20 mg BIW, and 10 mg TIW in combination with s.c. BTZ and Dex and to provide exposure, safety and efficacy data to identify the optimal regimen of PAN in a randomized, 3-arm parallel design. This study will also assess the impact of administering s.c. BTZ in combination with PAN and Dex twice weekly for 4 cycles, and then weekly starting from Cycle 5 until disease progression in patients 75 years of age. Patients 75 years of age will receive for the entire treatment period s.c. BTZ weekly in combination with PAN and Dex until disease progression. 