A 4 year old girl is diagnosed with Wilms' tumor. After surgical resection of her right kidney, she's started on an 18 month chemotherapy course. During the course of her chemotherapy, she starts to have polyuria, polydipsia and failure to thrive. Her control hemogram shows WBC: 7000 with normal differentiation, Hb: 11.9, Plt: 253,000. Her biochemistry panel is: Glucose: 84 (fasting), BUN: 14, Cr: 0.45, AST: 24, ALT:19, Na:134, K:3.3, LDH: 400, Ca: 7,0, P: 1,9, uric acid: 2,1. Her urinary dipstick shows d: 1013, pH: 5, RBC: 0, WBC:0, protein: 2+, glucose: 2+. Capillary blood gas shows pH: 7.31, PaCO2: 30, HCO3-: 13. Her 24-hour urine sample reveals an increase in beta-2 microglobin, calcium, phosphorus, various aminoacids and sodium. What is the most likely etiology explaining her symptoms and lab findings?