[Persistent electrolyte deficiency in an oncology patient].

We report the case of a 47-year-old patient with a dedifferentiated mediastinal-thoracic liposarcoma who developed electrolyte disturbances during chemotherapy with Ifosfamide and Doxorubicin. Initially, a refeeding syndrome was suspected, supported by hypokalemia, hypomagnesemia, and hypophosphatemia. However, the prolonged course of electrolyte abnormalities, along with the presence of normoglycemic glucosuria and proteinuria, were not consistent with this diagnosis. Over time, a partial Fanconi syndrome was confirmed, reflecting a proximal tubular dysfunction - a well-known complication of Ifosfamide therapy. Notably, standard markers of kidney function, such as eGFR, remained within normal limits early in the course, highlighting the importance of sensitive early indicators like electrolyte abnormalities and glucosuria. Early urine diagnostics (ideally prior to the initiation of electrolyte replacement) are essential for recognizing and classifying this potentially serious adverse effect.