Microscopic examination of a bone marrow biopsy in this patient would reveal predominantly:

Multiple myeloma is a clonal proliferation of plasma cells producing monoclonal immunoglobulin. Classic tetrad (CRAB): hyperCalcemia, Renal failure, Anemia, Bone lesions (punched-out lytic lesions, including in the jaw and skull). Bence-Jones protein (light chains) in urine is characteristic.