Primary Pulmonary Osteosarcoma Presenting as a 1.7-cm Subpleural Nodule in a 61-Year-Old Man: A Case Report.

BACKGROUND Primary pulmonary osteosarcoma (PPOS) is rare and can mimic metastases or benign pulmonary nodules. We present a 1.7-cm PPOS and outline an imaging-pathology diagnostic workup. CASE REPORT A 61-year-old man with prior hepatocellular carcinoma (HCC) developed a right upper lobe subpleural nodule enlarging from 0.7 to 1.7 cm over 5 months. Positron emission tomography/computed tomography showed moderate uptake (SUVmax=5.2). Whole-body bone scintigraphy showed no skeletal lesions. Uniportal video-assisted thoracoscopic wedge resection with lymph node sampling was performed, with negative margins. Histologic examination revealed a spindle-cell sarcoma producing lace-like malignant osteoid with a focal chondroid matrix. Immunohistochemistry showed diffuse nuclear special AT-rich sequence-binding protein 2 (SATB2) positivity, with a Ki-67 index of approximately 30%, while epithelial, vascular, and solitary fibrous tumor markers were negative. Although HCC-specific immunohistochemistry was not performed, normal alpha-fetoprotein levels, the absence of hepatic recurrence on imaging, and the presence of malignant osteoid formation supported the exclusion of metastatic HCC. A final diagnosis of PPOS was made. The patient received adjuvant liposomal doxorubicin plus cisplatin and, to date, remained disease-free 9 months after surgery. CONCLUSIONS PPOS can present as a lesion smaller than 2 cm. An integrated imaging-pathology workup and early resection can yield favorable short-term outcomes.