TOPIC: Lung Cancer TYPE: Medical Student/Resident Case Reports INTRODUCTION: We present a case of a patient with acute respiratory failure due to cannon-ball appearance on chest imaging secondary to an interesting malignancy- stay tuned! CASE PRESENTATION: This is a case of a 79-year-old, former smoker male, with a history of prostate and testicular cancer who was in remission for many years. CT scan of the chest 1 year ago showed a calcified left lower lobe nodule (figure 2). He presented with dyspnea on exertion, ongoing for the past 3 months associated with chest congestion and a non-productive cough. Oxygen saturation at home dropped below 85%. He was afebrile, HR of 105, respiratory rate of 22, blood pressure of 147/69, and O2 sat. 93% at room air. COVID test was negative and chest x-ray showed multiple soft tissue masses throughout both lung fields (figure 2). CT angiography of chest was negative for pulmonary embolism and showed innumerable pulmonary masses and nodules throughout bilateral lung fields (figure 3 and 4). Prostate specific antigen, carcinoembryonic antigen, alpha-fetoprotein, and CA19-9 were negative. Lung biopsy reported pleomorphic sarcoma with osteoclast-like giant cells. Oncology planned to initiate chemotherapy as an outpatient, unfortunately, the patient was unstable for a PET-scan or further testing and failed treatments with Docetaxel and Gemcitabine. He eventually opted for comfort care and home hospice. DISCUSSION: Majority of sarcomas are soft tissue origin with some bony origin as well. They are mostly mesodermal with a minority arising from neuro-ectoderm cell lineage. The four most common malignant non-hematopoietic bone tumors are osteosarcoma, chondrosarcoma, Ewing's sarcoma, and malignant fibrous histiocytoma. Tumor cells, in our case, were positive for vimentin and CD-68 and negative for carcinoma, melanoma, and lymphoma stains, consistent with diagnosis of sarcoma. Cannon-ball presentation in lung can be due to metastatic disease, vasculitis, sarcoidosis, infections like tuberculosis, etc. Any malignancy with hematogenous spread can cause it, the most common being breast, colorectal, renal cell, sarcoma, and bladder cancers, etc. Our case is unique because we could not specify the primary origin of the sarcoma. No intra-abdominal malignancy was identified on CT imaging and the patient denied extremity pain or complaints consistent with vertebral or spinal cord involvement and extremity x-rays were negative for any obvious lesion, therefore, it is quite possible that this is a case of osteoclastic sarcoma of an unknown primary. CONCLUSIONS: This case illustrates the possibility of extensive metastasis from an osteoclastic sarcoma without an obvious primary. These can be very aggressive as seen in our patient and the present therapies may not be sufficient to manage them and better understanding of the pathology and therapeutics is necessary. REFERENCE #1: Siegel RL, Miller KD, Fuchs HE, Jemal A. Cancer Statistics, 2021. CA: A Cancer Journal for Clinicians 2021;DISCLOSURES: No relevant relationships by Gnananandh Jayaraman, source=Web Response No relevant relationships by Danish Khatri, source=Web Response No relevant relationships by Tusharkumar Pansuriya, source=Web Response No relevant relationships by Syed Talha Qasmi, source=Web Response No relevant relationships by Sivatej Sarva, source=Web Response