A 67-year-old male presents with 3 months of lumbosacral pain and weight loss. Blood pressure (BP) is normal. There is lumbar spine tenderness and bilateral lower extremity edema. Hemoglobin (Hb) is 62g/L, urinary protein ++++, serum calcium (Ca) 4.6mmol/L, alkaline phosphatase 280U/L, and γ-globulin 45%. The most likely type of proteinuria is: