Lim, Tristan

Abstract Immune checkpoint inhibitor–associated immune thrombocytopenia (ICI-ITP) has been described in case reports and small case series, but comprehensive data on its incidence, risk factors, clinical features, treatment, and outcomes are lacking. We reviewed medical records of all adults initiating ICI therapy between 2016 and 2023 at 29 US hospitals across 7 major cancer centers to identify patients with ICI-ITP. Multivariable logistic regression was used to identify risk factors, and Cox modeling was performed to assess the association between ICI-ITP, its severity, and mortality. Among 86 467 patients, ICI-ITP occurred in 214 (0.25%). Independent risk factors included lower baseline platelet count, combination ICI therapy, stage IV cancer, and additional immune-related adverse events. ICI-ITP occurred at a median of 8 weeks (interquartile range [IQR], 4-18) after ICI initiation, with a median nadir platelet count of 41 × 109/L (IQR, 17 × 109/L to 64 × 109/L). Patients were treated with glucocorticoids (n = 106 [49.5%]), immune globulin (n = 39 [18.2%]), and thrombopoietin receptor agonists (n = 29 [13.6%]). Recovery occurred in 161 patients (75.2%) at a median of 2.3 weeks (IQR, 1.0-5.3). Of 76 patients rechallenged with ICIs, 23 (30.3%) developed recurrent ICI-ITP. ICI-ITP and its severity were associated with higher all-cause mortality, with a nearly threefold increase in risk among patients with severe ICI-ITP than those without ICI-ITP (adjusted hazard ratio, 2.96 [95% confidence interval, 2.14-4.08]). These findings establish ICI-ITP as a rare but clinically significant complication of ICI therapy, provide, to our knowledge, the first large-scale description of its risk factors and clinical course, and underscore the importance of timely recognition and management.

Abstract INTRODUCTION Immune checkpoint inhibitors (ICIs) have emerged as a cornerstone of cancer therapy. However, despite their efficacy, ICIs can cause a unique spectrum of autoimmune toxicities known as immune-related adverse events (irAEs). In contrast to irAEs involving other organ systems, hematologic irAEs such as ICI-associated immune thrombocytopenia (ICI-ITP) are less common. As a result, existing data on ICI-ITP are largely confined to isolated case reports, single-center case series, and pharmacovigilance databases lacking granular clinical data. To address this key knowledge gap, we sought to comprehensively characterize the incidence, risk factors, clinical features, treatments, and outcomes associated with ICI-ITP. METHODS We performed a multicenter cohort study of adult patients who initiated ICI therapy at 29 hospitals across 7 major cancer centers in 11 geographically diverse states in the US between 2016-2023. ICI-ITP was defined as a decline in platelet count to <100 x109/L in the absence of an alternative more plausible etiology of thrombocytopenia. Patients with hematologic malignancies were excluded, as were those who received cytotoxic chemotherapy within 30 days prior to thrombocytopenia onset. For each patient identified as having ICI-ITP, we collected data on demographics, comorbidities, medications, laboratory values, treatments, and outcomes. All data were extracted by manual chart review. To identify risk factors for ICI-ITP and to examine its association with death, for each case of ICI-ITP we also collected data on two control patients who initiated ICI therapy at the same site and in the same year but without development of ICI-ITP. We used multivariable logistic regression to identify independent risk factors for ICI-ITP and its recovery (the latter defined according to criteria established by the ITP International Working Group). We used a multivariable Cox model to examine the association between ICI-ITP and its severity with all-cause mortality. RESULTS We identified a total of 214 patients who developed ICI-ITP among 86,648 examined (0.25%). The incidence was highly consistent across sites (range, 0.15–0.30%). Risk factors for ICI-ITP included simultaneous receipt of two different classes of ICIs, additional irAEs, and a lower baseline platelet count. ICI-ITP developed at a median of 8 weeks (IQR, 4–18) following ICI initiation. The median nadir platelet count was 41 x109/L (IQR, 17–64). Six out of 214 patients (2.8%) developed a major bleed, and 16 patients (7.5%) developed a clinically relevant non-major bleed. Cell-bound anti-platelet antibody testing was positive in 6 of 8 patients (75.0%) for whom it was assessed, and median circulating thrombopoietin levels (201 pg/mL [IQR, 178–295]) were similar to those seen in primary ITP. Treatments used included glucocorticoids (49.5%), immune globulin (18.2%), and thrombopoietin receptor agonists (13.6%). Overall, 161 patients (75.2%) recovered from ICI-ITP at a median of 2 weeks (IQR, 1–5) following ICI-ITP onset. Predictors of recovery included additional irAEs and a higher nadir platelet count. Treatment response was observed in 57.0%, 56.4%, and 58.3% of patients within 60 days following initiation of glucocorticoids, immune globulin, and thrombopoietin receptor agonists, respectively. Of 76 patients rechallenged with an ICI, 23 (30.3%) developed recurrent ICI-ITP at a median of 9 weeks (IQR, 2–15); 17 of these 23 patients (73.9%) recovered. Finally, ICI-ITP and its severity were monotonically associated with a higher risk of death (adjusted hazard ratio 2.96 [95% CI, 2.14–4.08] for those with severe ICI-ITP compared to those without ICI-ITP). CONCLUSION In this multicenter study involving patients treated with ICIs at 29 hospitals across the US, we identified 214 patients with ICI-ITP. For the first time, we characterize in detail the incidence, risk factors, clinical features, treatments, and outcomes of ICI-ITP, a relatively novel disease entity. We found that more than half of patients responded to conventional ITP-directed therapies, and that most patients rechallenged did not develop recurrent ICI-ITP. We also found that ICI-ITP was independently associated with an increased risk of death, including a nearly 3-fold increased risk in those with severe ICI-ITP. These findings highlight ICI-ITP as a rare but clinically significant complication of ICI therapy that hematologists must be equipped to recognize and manage.

Importance The use of immune checkpoint inhibitors (ICIs) is increasing. Little is known about the frequency of late-onset immune-related adverse events (irAEs) and the patient-specific risk factors associated with their development. Objectives To assess the incidence of persistent or de novo late-onset irAEs requiring hospitalization and identify patient factors associated with risk of late-onset irAEs. Design, Setting, and Participants This retrospective observational cohort study conducted from January 2011 to October 2022 included patients who received ICIs and were hospitalized with irAEs at an academic medical center. Exclusion criteria included ICI therapy outside of the hospital system and no irAE diagnosis during admission. Data were analyzed from November 15, 2022, to January 8, 2025. Exposure Late-onset irAEs. Main Outcomes and Measures The main study outcomes were (1) incidence of irAE hospitalization at 0 to 6 months (early), more than 6 to 12 months (intermediate), and more than 12 months (late) after ICI initiation and (2) patient factors associated with risk of late-onset irAEs. Results Among the 795 patients hospitalized with irAEs, the median age was 67.3 years (IQR, 58.3-74.8 years); 476 (59.9%) were male. Most patients (n = 517 [65.0%]) received anti–programmed death ligand 1 (PD-L1) and anti–programmed cell death 1 monotherapy, with the most common indications being melanoma (n = 335 [42.1%]) and lung cancer (n = 167 [21.0%]). The median time from start of ICI therapy to hospital admission was 2.7 months (IQR, 1.2-6.1 months), with 14.7% of patients (n = 117 of 795) presenting 6 to 12 months after initial ICI exposure and 10.8% of patients (86 of 795) presenting more than 12 months after initial exposure. The irAEs most likely to present late included those involving the kidney (10 of 32 [31.3%]) and hematologic (5 of 23 [21.7%]) organ systems. In univariate analysis, ICI type was significantly associated with the timing of hospital admission for irAEs; of the 517 patients receiving anti–PD-L1–based therapy, 13.5% (n = 70) presented late compared with 5.4% (9 of 167) receiving dual therapy with anti–cytotoxic T-lymphocyte–associated protein 4 ( P < .001). Patients receiving perioperative ICI therapy were significantly more likely to be admitted at the intermediate interval (16 of 68 [23.5%]) compared with those with metastatic disease (87 of 678 [12.8%]) ( P = .03). Timing of irAE was also significantly associated with active ICI exposure; among the patients presenting late, 7.4% (48 of 651) had received ICI therapy within the last 60 days compared with 26.4% (38 of 144) who had not had recent ICI exposure ( P < .001). Conclusions and Relevance The findings of this retrospective observational cohort study suggest that late irAEs are possible, with a subset of patients presenting years after the start of ICI therapy. Clinicians must remain vigilant for irAEs regardless of elapsed time from ICI therapy, especially as patients live longer and ICIs become more widely used. Future investigations are needed to better understand the risk factors for late-onset irAEs and the distinct immunologic pathways that underlie such events.