Impact of CYP and ABCB1 Polymorphisms on Bortezomib-Induced Adverse Events in Multiple Myeloma

Purpose: Bortezomib (BTZ) is widely used in multiple myeloma (MM), but its toxicity shows marked interindividual variability. This study aimed to identify pharmacogenetic and clinical factors associated with BTZ-related adverse drug reactions (ADRs). Methods: A retrospective and prospective observational study was conducted in 127 MM patients treated with BTZ-based regimens. Polymorphisms in CYP enzymes and ABCB1 were genotyped using qPCR. Associations between genetic variants, treatment response, and ADRs were assessed using univariate and multivariate analyses with Benjamini–Hochberg correction. Results: ADRs occurred in 98.4% of patients, most commonly gastrointestinal toxicity (49%), general toxicity (46%), and peripheral neuropathy (39%). Women showed higher rates of gastrointestinal toxicity and non-peripheral neurotoxicity. Multivariate analysis identified the ABCB1 C1236T A/G genotype as protective against gastrointestinal toxicity, while the CYP3A4 intermediate metabolizer phenotype was associated with increased psychiatric toxicity. TP53 mutations were independently associated with hematologic and renal toxicity. Kaplan–Meier analysis showed earlier onset of peripheral neuropathy and respiratory toxicity in CYP3A4 intermediate and poor metabolizers. Conclusions: Genetic variation in ABCB1 and CYP3A4, together with clinical factors such as TP53 mutation and sex, may contribute to interindividual variability in BTZ safety in MM. These findings should be considered exploratory given the sample size and require confirmation in larger cohorts. Nonetheless, they suggest a potential role for pharmacogenomics in supporting future approaches to treatment personalization.