A rare case of miliary tuberculosis in a patient with NSCLC receiving PD1 inhibitor therapy, mimicking autoimmune pneumonitis.

Immune checkpoint inhibitors (ICIs) are widely used for the treatment of various types of cancer. One of the possible immune-related adverse effects of ICI is pneumonitis, which is a life-threatening condition that can present as a variety of radiographic patterns, so it can be difficult to differentiate from infectious cases of pneumonia based on radiological findings alone. We present a rare case of miliary tuberculosis (M. tuberculosis) in a patient receiving programmed death-1 (PD-1) inhibitor therapy mimicking autoimmune pneumonitis and possible pathophysiological mechanisms of this unexpected event. We presented a 52-year-old patient with stage IV non-small-cell lung carcinoma (NSCLC) who was admitted to the hospital with radiological and clinical signs of pneumonitis caused by immunotherapy-Pembrolizumab. During hospitalization, she was clinically, laboratory, and microbiologically processed and her diagnosis of M. tuberculosis was confirmed. Initial treatment started with corticosteroids as a pneumonitis treatment, and because there was no adequate response, and the diagnosis of tuberculosis was confirmed, treatment with a four-regimen antituberculotic drug started. On a control, CT scan regression in distribution and number of changes in lungs occurred. After a while, patient died due to hepatic failure. There are not many reported cases of pulmonary tuberculosis in patients receiving immunotherapy; to our knowledge, no cases of M. tuberculosis in a patient with lung cancer were described. Since there is a different approach to the treatment of tuberculosis and pneumonitis, we presented our dilemmas and literature review in this article. A multidisciplinary approach (oncologist, radiologist, microbiologist, etc.) is essential in a case like this.