Hypophosphatemia related to the use of ibrutinib

Introduction: Tyrosine kinase inhibitors (TKis) and Bruton's TKi (BTKis) constitute broadly used antitumor drug groups with almost completely tolerable and manageable side-effect profiles. Mainly side effects are cardiovascular and gastrointestinal for the TKi group. Hypophosphatemia is documented frequently in many studies with TKis but rarely mentioned with ibrutinib use up to the present. Case report: A 61-year-old patient with the diagnosis of chronic lymphocytic leukemia had hypophosphatemia-related complaints and symptoms when ibrutinib use was preferred for his second relapse of the disease. After drug discontinuation, we started ibrutinib again with an alternating dose. We managed to control hypophosphatemia, and the patient has been following up for 2 years in remission status without any support or a second drug need. Management and outcome: We have presented here a chronic lymphocytic leukemia case that developed mild–severe hypophosphatemia associated with ibrutinib use. By using an alternating dose of ibrutinib, we managed to control the disease and drug side effects. Discussion: TKis and BTKis are widely in use for different indications. Hypophosphatemia is rare but it can cause drug discontinuation or change if it is not manageable. It is mentioned that hypophosphatemia can be seen due to a common group effect with the mechanism of causing secondary hyperparathyroidism and renal tubulopathy. In our case, we could explain the side effect of hypophosphatemia with secondary hyperparathyroidism and renal tubulopathy. Prospective, large-group studies are needed to explain the hypophosphatemia and other side effects of ibrutinib and new BTKis in detail.