Hyperdense Pleural Metastasis from Osteosarcomatous Breast Phyllodes Tumor

Hyperdense pleural metastasis is rare, noting that high-density foci in the pleural space are commonly benign. We present a case of a 76-year-old female with past medical history of multicentric breast malignancy treated 5 years prior, who presented with unexpected weight loss. Chest CT demonstrated high-density foci in the left pleural space as well as a right lung nodule. There was no past medical history to support benign pleural etiologies of talc pleurodesis, asbesto-sis-related pleural plaques, and fibrothorax. However, the patient’s prior breast malignancy had included malignant phyllodes tumor with osteosarcomatous differentiation, in addition to invasive ductal carcinoma. On bone scan, the left hemithorax demonstrated intense radiotracer uptake, reflecting osteoid tissue, raising suspicion for osteosarcomatous pleural metastasis. This was supported by increasing left pleural lesions, as well as right lung biopsy demonstrating metastatic phyllodes with osteosarcomatous differentiation. Therefore, the hyperdense pleural lesions were determined to represent pleural metastasis from osteosarco-matous breast phyllodes tumor.