Year: 2026 | Month: July-September | Volume: 11 | Issue: 3 | Pages: 141-150
DOI: https://doi.org/10.52403/ijshr.20260317
Trastuzumab Induced Thrombocytopenia: A Case Series
Anirudh Singh1, Jaspreet Kaur1, Navaudhayam Ranganathan2, Anu Agrawal3, Vikas Yadav1
1Department of Radiation Oncology, Vardhman Mahavir Medical College & Safdarjung Hospital,
2Department of Radiation Oncology, AIIMS Rishikesh,
3Department of Radiation Oncology, Himalayan Institute of Medical Science, Dehradun
Corresponding Author: Dr. Anu Agrawal
ABSTRACT
Background: Trastuzumab is a cornerstone of treatment for HER2-positive malignancies and is generally well tolerated. While cardiotoxicity and infusion-related reactions are recognized adverse effects, trastuzumab-induced thrombocytopenia remains a rare complication, with fewer than 25 cases reported in the literature. We present a series of six patients with HER2-positive breast cancer who developed thrombocytopenia temporally associated with trastuzumab therapy.
Methods: A retrospective review was conducted at a tertiary cancer center to identify patients who developed thrombocytopenia during trastuzumab therapy between 2020 and 2025. Histopathologically confirmed HER2-positive breast cancer patients receiving trastuzumab were included. All patients underwent evaluation for alternative causes of thrombocytopenia, including peripheral smear examination, coagulation studies, viral markers, and bone marrow assessment. Drug causality was assessed using the Naranjo Adverse Drug Reaction Probability Scale.
Results: Six patients were identified. Median age was 46 years (range, 39–52 years). Thrombocytopenia developed after a median of 3.5 trastuzumab cycles (range, 2–7 cycles), with onset occurring 1–3 weeks following exposure. Median nadir platelet count was 51 × 10⁹/L (range, 30–63 × 10⁹/L). Four patients (66.7%) developed CTCAE grade 2 thrombocytopenia and two (33.3%) developed grade 3 thrombocytopenia. Naranjo scores ranged from 5 to 8, supporting probable drug causality. All patients received corticosteroids, two additionally received thrombopoietin receptor agonists, and one required platelet transfusion. Platelet recovery was observed in all patients, with a median recovery time of 10 days (range, 5–20 days). All 6 patients experienced recurrent episodes following subsequent trastuzumab exposures, however, four patients successfully completed all 17 planned trastuzumab cycles with appropriate supportive management.
Conclusions: Trastuzumab-induced thrombocytopenia is an uncommon but clinically significant adverse event that may occur after multiple uneventful treatment cycles and can recur with subsequent exposures. Unlike most published reports describing profound thrombocytopenia shortly after initial trastuzumab administration, our series demonstrates a milder but recurrent pattern of toxicity. Early recognition, exclusion of alternative etiologies, and individualized supportive management may permit continuation of trastuzumab therapy in selected patients.
Keywords: Trastuzumab, HER2-positive breast cancer, Breast cancer, Thrombocytopenia, Case report, Platelet transfusion, Chemotherapy, Drug-induced thrombocytopenia, Targeted therapy, Radiation therapy