Bruton’s tyrosine kinase (BTK) is a member of the tyrosine kinase expressed in hepatocellular carcinoma (TEC) family, and as a key kinase in the B cell receptor pathway (1, 2). BTK plays a critical role in various pivotal signaling processes in vivo, including B cell proliferation, trafficking, chemotaxis, and adhesion (3). Based on the crucial role of BTK, abnormalities in BTK can lead to chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma, mantle cell lymphoma (MCL), Waldenström’s macroglobulinemia, and so on (4–6). Therefore, BTK has become an essential target for treating B-cell malignancies.

In 2013, the FDA approved the marketing of ibrutinib, the first BTK inhibitor developed by Johnson Johnson and Pharmacyclics. The 2nd-generation BTK inhibitor acalabrutinib, developed by AstraZeneca, was approved for marketing by the FDA in 2017. In 2019, the Chinese pharmaceutical company BeiGene developed a Bruton’s tyrosine kinase inhibitor (BTKi) called zanubrutinib (7). In addition to this, BTKis that have been approved for marketing are tirabrutinib (8), orelabrutinib (9), and pirtobrutinib. However, due to the small number of reports in this study, they were not included to avoid unstable signals and an increase in false positive signals. Adverse drug events (ADEs) of BTKis are diverse and are concentrated in the cardiac system, dermatologic system, gastrointestinal system, infection-related, and bleeding-related ADEs (10). Currently, some studies have applied the FDA Adverse Event Reporting System (FAERS) to compare the safety of three BTKis in the occurrence of cardiac risks (11), urinary tract infection (12), and bleeding ADEs (13). A study also analyzed the safety of BTKis alone and in combination with other chemotherapeutic agents (14). There are no studies that have analyzed the post-marketing safety of BTKis using data from VigiBase (15), which is the world’s largest ADE reporting system. In this study, the safety of three BTKis will be analyzed at the system organ class (SOC), standardized medical dictionary for regulatory activities (MedDRA) queries (SMQ), and preferred term (PT) levels using two of the world’s largest spontaneous reporting systems (SRSs), FAERS and VigiBase. Hemorrhagic events are a major safety concern in targeted cancer therapy, as they may lead to treatment interruption, disease progression, or death (16). Patients receiving BTKis often require concomitant antithrombotic therapy for atrial fibrillation (AF), ischemic heart disease, or venous thromboembolism—conditions that may themselves be precipitated or exacerbated by BTK inhibition (17). The concomitant use of BTKis with anticoagulant or antiplatelet agents produces additive impairment of hemostasis, markedly increasing the risk of severe bleeding complications (18, 19). So we also analyzed the risk of bleeding when BTKis are used alone or in combination with anticoagulants/antiplatelets, which is expected to provide more data support and further reference for the safe and rational use of BTKis in clinical practice.

This study is a comprehensive analysis that utilizes two of the largest SRSs in the world to characterize the safety profile of BTKis in multiple ways. Analyzing the risk of ADEs for three BTKis at different levels and in combination with anticoagulant/antiplatelet agents provides more comprehensive data to support the safe use of BTKis.

Regarding cardiotoxicity, the second-generation BTKis acalabrutinib and zanubrutinib significantly reduced the risk of AF compared to ibrutinib, consistent with evidence from previous clinical trials. This divergence may stem from their enhanced kinase selectivity: ibrutinib exhibits off-target inhibition of TEC family kinases and HER2/HER4 receptors due to lower selectivity, whereas zanubrutinib and acalabrutinib selectively target BTK with minimal HER2 interaction (24, 25). HER2/HER4 play critical roles in myocardial electrical activity and contractile function: HER2/HER4 heterodimerization is a key mechanism for maintaining cardiac signaling, and ibrutinib’s irreversible inhibition of these kinases may trigger myocardial dysfunction (26, 27). Additionally, TEC kinase inhibition may reduce PI3K-AKT signaling in cardiomyocytes, indirectly promoting arrhythmias (24). In contrast, zanubrutinib and acalabrutinib exhibit higher target selectivity: both inhibit HER4 and TEC but not HER2, and differences in TEC inhibition strength do not significantly increase cardiovascular toxicity. Since HER2 is a core driver of ibrutinib-associated AF, avoiding this target by second-generation drugs results in markedly lower AF risk (26). However, it is essential to note that ibrutinib’s broad kinase inhibition leads to significant AF, while acalabrutinib, despite its higher selectivity, shows prominent cardiac toxicity signals. Zanubrutinib generally poses lower risks but requires attention to specific atrial flutter cases.

In the vascular disorders, bleeding and hypertension were the most frequently reported ADEs across all three BTKis. Both acalabrutinib and zanubrutinib were associated with a lower proportion of bleeding events compared to ibrutinib. Previous studies have demonstrated that ibrutinib significantly increases the risk of severe and overall bleeding (16, 28–31), which is largely attributed to its effects on multiple signaling pathways. For second-generation BTKis, a meta-analysis of ten studies indicated that acalabrutinib significantly increases the risk of overall bleeding, but not severe bleeding (16). Furthermore, two head-to-head phase III multicenter trials—comparing zanubrutinib vs. ibrutinib and acalabrutinib vs. ibrutinib, respectively—showed that both acalabrutinib and zanubrutinib were associated with a reduced risk of overall bleeding compared to ibrutinib, with no significant differences observed in the incidence of severe bleeding (32, 33). BTK is essential in BT/VWF-mediated aggregation-induced thromboxane A2 generation and GPIb-dependent stabilization of arterial thrombus formation in vivo (34). Additionally, TEC family kinases, also substrates of ibrutinib, contribute to the downstream regulation of phospholipase Cγ2 (PLCγ2) via the collagen receptor glycoprotein VI (GPVI) on human platelets. Both Tec and BTK are required for platelet activation via GPVI, and Tec has been shown to compensate for BTK deficiency in the regulation of PLCγ2 (35, 36). Moreover, ibrutinib inhibits several intracellular signaling molecules critical for platelet function, including members of the SRC family kinases and JAK3. Inhibition of SRC by BTKis has been linked to impaired platelet aggregation and hemostasis, contributing to increased bleeding risk (16, 37). Although both acalabrutinib and zanubrutinib are also irreversible BTKis capable of selectively inhibiting BTK and Tec at low concentrations in platelets—thereby attenuating low-level GPVI-mediated platelet activation—they do not exhibit the broader off-target inhibition observed with ibrutinib. In particular, they do not significantly inhibit SRC family kinases, which play a central role in platelet signaling. Previous studies have highlighted substantial differences among the three agents’ effects on platelet function (38, 39).

In addition, our study suggests that there is a risk of bleeding when ibrutinib is combined with either anticoagulant or antiplatelet agents. Previous studies have found that about half of patients on ibrutinib develop mild to moderate platelet dysfunction, and this effect is exacerbated when combined with antiplatelet agents (40). Populations typically treated with BTKi drugs, such as those with CLL, MCL, and MZL, often have comorbidities, and there is a recognized risk of new-onset AF associated with BTKis use. Clinicians usually face challenges in treatment decision-making when combining ibrutinib with oral anticoagulants (41). Studies have suggested that acalabrutinib has superior safety characteristics concerning bleeding ADEs, particularly in patients with low sensitivity to platelet aggregation induced by ibrutinib (42), suggesting that switching BTKis in clinical practice may not reduce the risk of bleeding in all patients. Current expert consensus recommends avoiding the concomitant use of potent antiplatelet or anticoagulant agents during BTKi therapy whenever possible. If antithrombotic therapy is necessary, treatment should be initiated with a low-dose BTKi, with cautious dose escalation under close monitoring. For patients undergoing surgery or at high risk of bleeding, temporary discontinuation of BTKis for 3–7 days before and after the procedure is advised. Moreover, when combining BTKis with antithrombotic agents, an individualized risk–benefit assessment should be conducted, balancing thrombotic protection against bleeding risk and considering patient-specific comorbidities (43).

ADEs reports associated with blood and lymphatic system disorders accounted for a large proportion of all ADEs associated with BTKis and showed a high signal intensity. Abnormalities in various tests are frequently concentrated in blood-related examinations. In the usage of all three drugs, signals for abnormal platelet, white blood cell (WBC), and neutrophil counts were reported. In two head-to-head studies, hematologic toxicity had a high incidence among all ADEs. However, acalabrutinib and zanubrutinib did not demonstrate a significant advantage over the first-generation BTKis, ibrutinib, in reducing hematologic toxicity (32, 33). Other real-world studies have also monitored new hematological ADEs, such as splenomegaly and lymphadenopathy. Splenomegaly may affect blood filtration and immune function, while lymphadenopathy suggests potential local or systemic immune response abnormalities (44). It is essential to closely monitor patients’ immune and coagulation functions to prevent serious ADEs like bleeding or infection. In clinical practice, it is recommended to routinely conduct complete blood cell count tests before and during treatment, focusing on monitoring WBC count, platelet count, red blood cell count, and bleeding tendency assessment. If severe hematologic toxicity occurs, BTKi therapy should be paused, and treatment regimens should be adjusted based on the patient’s characteristics and risk-benefit assessment to ensure medication safety (43).

Infectious complications represent another critical category of ADEs associated with BTKi therapy. Overall, all three BTKis were associated with various types of infections. However, in terms of signal strength, the second-generation agents demonstrated a markedly reduced risk of infection-related ADEs compared to the first-generation inhibitor, ibrutinib. Across multiple SOC, including the central nervous system, lungs, skin, and systemic infections, there was a notable increase in the risk of infections caused by specific pathogens. Among these, aspergillus infections were particularly prominent. These findings suggest that patients receiving BTKi therapy, regardless of the generation of the agent, may be at elevated risk for aspergillosis. As such, preventing and managing aspergillus infections should be an important consideration in clinical practice when using these agents. Due to various disease-associated innate and adaptive immune deficiencies, patients with B-cell malignancies are particularly susceptible to infections. A meta-analysis has shown that ibrutinib use is significantly associated with an increased risk of infections in this patient population (45). A systematic review of 44 studies reported that 56% of patients receiving ibrutinib monotherapy and 52% of those receiving combination therapy experienced infection-related ADEs. Notably, approximately one-fifth of patients developed pneumonia (45, 46). The interference with BTK and interleukin-2-inducible T cell kinase signaling pathways in immune cells is considered a key mechanism underlying the increased susceptibility to infections observed with ibrutinib. Several reports have highlighted a particularly high risk of fungal infections, including invasive aspergillosis, associated with ibrutinib use—findings that are consistent with the results of our study (45). A signal was detected only for ibrutinib in a real-world research study specifically investigating the risk of urinary tract infections associated with BTKis treatment. The authors suggested that differences in marketing timelines among the three agents and the greater use of second-generation BTKis as first-line therapies, often in patients with relatively preserved immune function, may significantly influence the detection and reporting of infection-related ADE signals (12).

The impact of medications on liver and kidney function has always been an important area of concern. All three BTKis mention potential hepatotoxicity and nephrotoxicity in their product labels. In our study, we observed a small number of signals related to hepatotoxicity and renal impairment, but their signal strength was at the threshold level, suggesting weak statistical associations. Although these signals may reflect potential risks, their clinical significance should be interpreted cautiously, as they did not reach the threshold for significance. It is advisable to further verify these findings through laboratory tests, dose-dependency analyses, and long-term follow-up data. However, we also identified a few signals that may warrant attention. While the majority of renal-related ADEs were associated with bleeding and infections, such as hematuria and urinary tract infection, we observed a signal for fluid retention in both ibrutinib and zanubrutinib, with a stronger signal in ibrutinib. This suggests that attention to patients’ fluid status may be necessary when using these agents. In the liver system, we identified a signal for hepatitis B reactivation in both zanubrutinib and ibrutinib. This ADE may be related to immune suppression caused by BTKi therapy, rather than a direct hepatotoxic effect (47).

Regarding other systems, we also identified several less frequently mentioned ADEs signals. For example, ibrutinib was associated with middle ear effusion and deafness, while both acalabrutinib and ibrutinib showed signals for glaucoma and iron deficiency. Additionally, all three BTKis were linked to dehydration and appetite disorders. We also observed general disorders such as fatigue and tiredness across the three medications. In clinical practice, it is essential to conduct a multidimensional assessment based on the individual characteristics of patients, combining their baseline conditions with close dynamic monitoring. This approach will help identify ADE signals and optimize treatment strategies, ensuring continuity of care while improving patients’ quality of life.

Our study, like other pharmacovigilance studies, has several limitations. Firstly, there is an inherent bias in the data sources; SRSs may suffer from underreporting, duplicate reporting, and misreporting, and serious or new ADEs are more likely to be reported, whereas minor or common events may be underestimated. This could lead to an increased reporting rate of serious or more closely monitored ADEs over time, amplifying imbalances and thereby exaggerating differences between drugs. Second, the data sources for SRS are variable. FAERS data primarily originates from the United States, while VigiBase data is collected globally. Differences in data collection and processing methods, as well as variations in population bases, may account for discrepancies between signals observed in FAERS and VigiBase. Finally, even if the results of disproportionality analyses are significant, they are unlikely to confirm a causal relationship between drugs and ADEs and represent only a statistical association, a more definite causal relationship requires further verification.