RESUMEN
Trastuzumab is a humanized monoclonal antibody against human epidermal growth factor, useful in breast cancer. It is well tolerated but sometimes may associate with significant adverse effects. Sarcoidosis is a granulomatous disease involving multiple organs with poorly understood aetiology. Mediastinal lymphadenopathy is the most common presenting feature of Sarcoidosis. Reported cases of Sarcoidosis associated with Trastuzumab are quite less in number. High degree of suspicion of the above is thought of in a scenario of malignancy patients receiving chemotherapy. Newly appearing FDG avid lymph node in PET scan may give first impression of metastasis and treatment failure or infection. However correct diagnosis is a must (differentiating metastasis, treatment failure or infection) to provide correct treatment and avoid side effects of inappropriate therapies. Correct diagnosis also helps in appropriate prognostication and unnecessary stoppage of Trastuzumab. Here we are describing Sarcoidosis associated with Trastuzumab in a patient with breast cancer.