[Evaluation of Ixazomib Relative Dose Intensity for IRd Therapy in Elderly Patients with Relapsed or Refractory...

Ixazomib (IXA) is a convenient oral anticancer drug; however, due to its fixed dosage, IXA tolerability among elderly Japanese individuals may be reduced. Therefore, this study aimed to clarify the difference in relative dose intensity (RDI) of IXA in IRd therapy in elderly patients. Between October 2018 and September 2023, patients who underwent IRd therapy (IXA, lenalidomide, and dexamethasone combination treatment) at Ogaki Municipal Hospital were enrolled in the study and categorized into two age groups: ≥75 years (group O, n=16) and <75 years (group Y, n=6). We retrospectively analyzed RDI of IXA, in IRd therapy. In addition, we evaluated the reasons for dose reduction or delayed treatment. The median initial IXA dose was 3 mg (range: 2.3-4 mg) and 4 mg (range: 3-4 mg) in group O and Y, respectively (p=0.122). The median RDI in group O (65.8%, range: 51.1-91.7%) was significantly lower than in group Y (93.3%, range: 80.5-100.0%) (p=0.002). Among them, anorexia was more common in group O than in group Y (p=0.049). In group O, dose adjustments were made due to anorexia (n=10), diarrhea (n=5), nausea (n=2), and fatigue (n=2). In group Y, adjustments were made due to diarrhea (n=2) and thrombocytopenia (n=1). Upon IXA (4 mg) administration, the rate of dose adjustments due to gastrointestinal symptoms were 75% and 17% in group O and Y, respectively (p=0.051). Overall, RDI was lower in group O owing to gastrointestinal symptoms. This suggests that the fixed IXA dosage (4 mg) is less tolerable in older individuals.