A 62-year-old male presents with back pain for 6 months. X-rays of the thoracic/lumbar spine and ribs show wedge-shaped compression of T10, L1, and L3 vertebrae, along with multiple osteolytic rib lesions. Lab results: Hb 82g/L (anemia), ESR 96mm/h, urinary protein (+++), negative Bence-Jones protein, albumin 31g/L, globulin 62g/L. The most likely diagnosis is: