Urine Xanthine Crystals in Tumor Lysis Syndrome.

Urine xanthine crystals are remarkably rare but can be observed by routine urine microscopy. We report the results of a 67-year-old man with T-cell-prolymphocytic leukemia whose urine contained xanthine crystals after chemotherapy and prophylactic administration of febuxostat. Accumulation of xanthine was due to tumor lysis syndrome causing a massive release of DNA. The metabolized DNA caused an increase of xanthine, which was not readily converted to uric acid by xanthine oxidase because of febuxostat inhibition of this enzyme.