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 6 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.