 Approximately 340 male or female patients aged 18 or older suffering from hematologic malignancies de novo patients or relapsing patients at intermediate to high risk of TLS and scheduled for receiving the first cycle of cytotoxic chemotherapy, regardless of the line of treatment, will be randomized in this study. Eligible patients as per screening visit will be randomly allocated in a 1:1 ratio to Febuxostat or Allopurinol. The double-blind treatment period starts two days prior to the planned beginning of chemotherapy and continues for 7 to 9 consecutive days, according to Investigator judgment and on the basis of the actual duration of chemotherapy regimen administered to the patient. Along the study treatment, uric acid levels, creatinine levels, Laboratory TLSClinical TLS and Adverse Events represent the major clinical findings to be monitored on a daily basis. Overall the study encompasses 10 to 11 planned visits at site, including screening, randomisation, on treatment and final follow up visits. 