e23379 Background: Trastuzumab, alone or with pertuzumab, is standard adjuvant therapy for HER2-positive breast cancer. Real-world evidence describing the incidence, clinical course, and management impact of trastuzumab-induced thrombocytopenia (TIT) is limited. Methods: Multicenter retrospective cohort study across three UAE infusion centers (2016–2024). Electronic records of 87 women receiving adjuvant trastuzumab (IV/SC; originator or biosimilar) with or without pertuzumab were reviewed. All patients had platelet recovery after (neo) adjuvant chemotherapy (baseline > 150×10⁹/L). TIT was defined as any platelet count 90% continued HER2-targeted therapy without interruption; cycle postponement occurred in 2. 5%, pertuzumab discontinuation in 2. 5%, and regimen change in 1. 3%. TIT incidence was similar with trastuzumab+pertuzumab vs trastuzumab alone (36. 8% vs 31. 6%; p = 0. 68). No baseline demographic, stage, comorbidity, formulation, or regimen variables were associated with TIT risk. Conclusions: In this real-world multicenter UAE cohort, adjuvant trastuzumab ± pertuzumab was associated with a moderate rate of laboratory-defined thrombocytopenia that was usually early-onset and low-grade, with infrequent transfusion or treatment modification, although recurrence occurred in a meaningful minority. Routine platelet monitoring is appropriate; severe or treatment-limiting events appear rare. Logistic regression predicting thrombocytopenia. Predictor Adjusted OR 95% CI p Stage I (vs. II) 0. 00 0. 00 – ∞. 949 Stage III (vs. II) 1. 09 0. 32 – 3. 72. 890 Regimen: Phesgo SC (vs. Trastuzumab alone) 0. 65 0. 10 – 4. 17. 646 Regimen: T+P IV (vs. Trastuzumab alone) 0. 74 0. 17 – 3. 17. 686 Age (per year) 1. 01 0. 94 – 1. 07. 837 Weight (per kg) 0. 99 0. 95 – 1. 03. 540 Number of cycles 1. 02 0. 93 – 1. 12. 711 Chronic disease (yes vs. no) 0. 87 0. 24 – 3. 10. 828 Baseline platelets <150 3. 94 0. 29 – 54. 35. 305 Note. OR = odds ratio; CI = confidence interval. Reference groups: Stage II, Trastuzumab alone.
Abdaljalil et al. (Thu,) studied this question.