Interstitial lung disease associated with trastuzumab monotherapy: A report of 3 cases

We herein report 3 cases of female patients with breast cancer who developed interstitial lung disease (ILD) during trastuzumab monotherapy in an adjuvant setting. Prior chemotherapy included 4 cycles of epirubicin and cyclophosphamide in patients 1 and 2, and 4 cycles of docetaxel, cyclophosphamide and trastuzumab in patient 3. Patient 1 presented with a cough and fever after the fourth cycle of trastuzumab. Patient 2 experienced rapid deterioration of oxygen saturation without subjective symptoms within 3 h of the first administration of trastuzumab. Patient 3 was unexpectedly diagnosed with organizing pneumonia in a scheduled computed tomography (CT) scan after the first course of trastuzumab. Based on clinical data, such as decreased PaO₂ level, increased serum levels of KL-6 and/or lactate dehydrogenase, and findings on chest CT, these patients were diagnosed with drug-induced ILD. Considering the clinical course, trastuzumab was incriminated as the cause of ILD, particularly in patients 1 and 2. All 3 patients improved due to the timely diagnosis, discontinuation of trastuzumab and immediate administration of corticosteroid therapy. Although ILD is a rare adverse event associated with trastuzumab, it may cause rapid deterioration without preceding symptoms. Close observation and early diagnosis are required to avoid an unfavorable outcome.