A rapidly developing lung mass diagnosed as desmoplastic small round cell tumor.

We present a case of a young male who presented with complaints of fever along with cough and sputum. He was diagnosed with having right pleural effusion. He was already taking anti-tubercular therapy for one month before presentation. He was started on intravenous antibiotics and continued on anti-tubercular therapy in our hospital, based on his high leukocyte count, pleural fluid analysis, and ultrasonographic report of multiple hypoechoic areas in the liver. His symptoms continued to worsen and he subsequently developed mediastinal widening and a left lung mass. Commuted tomography (CT)-guided biopsy of the lung mass revealed a desmoplastic small-round-cell tumor. Desmoplastic small-round-cell tumor is a rare and aggressive tumor, which presents rarely as a mediastinal and lung mass. This tumor has very poor prognosis.