Pneumonitis associated with Trastuzumab emtansine in a patient with metastatic breast cancer

Introduction Trastuzumab emtansine (TDM-1) is an antibody–drug conjugate effective in human epidermal growth factor receptor-2 - expressing advanced breast cancer. Pulmonary complications of TDM-1 are rarely reported. TDM-1-associated interstitial lung disease is referred to as pneumonitis. Case report A 47-year-old female patient who underwent modified radical mastectomy and axillary lymph node dissection operations due to a palpable mass in the right breast and axillary region. The patient who had received multiple chemotherapy was last receiving TDM-1 treatment. Fatigue, dyspnea, and tachypnea were detected for the first time on 20 days after the 6th treatment. Menagement and outcome In our case, we first considered metastasis, pneumonia and fungal infection based on radiological findings, but the lack of response to the treatments and the results of the investigations suggested drug-induced pneumonia and steroid treatment was started. Our case had a complete radiological recovery and complete response to sterod therapy. In such cases, it is important to first exclude infections and metastasis. In cases of drug-induced pneumonia, the first treatment option is systemic corticosteroids and generally responded well. Discussion Unlike other cases of interstitial pneumonia, lung imaging of our case was resembling a metastasis, pneumonia and fungal infection. With increasing use of TDM-1, we will have more experience in both efficacy and complications of TDM-1. Although TDM-1 is a well-tolerated drug, clinicians should be aware of rare pulmonary complications and prepared to respond appropriately.