Pulmonary Tumor Thrombotic Microangiopathy (PTTM) is a fatal complication of malignancy characterized by embolization of tumor cells to the pulmonary vasculature leading to a vascular reaction resulting in stenosis and pulmonary hypertension. Because the clinical manifestations of PTTM overlap with those of other entities, premortem diagnosis is challenging. We describe an unusual case of PTTM as the only clinical manifestation of recurrent metastatic breast cancer. A 50 year-old woman presented with hypoxemia and echocardiographic findings consistent with pulmonary hypertension and cor pulmonale. Correlation of premortem pulmonary imaging with autopsy histopathologic findings revealed that ill-defined ground-glass opacities identified on CT angiogram corresponded to areas of cellular interstitial fibrosis and widespread intrapulmonary tumor emboli involving predominantly small-sized arteries with associated florid intimal fibrosis. The radiologic nodularities and scattered peripheral wedge-shaped consolidations corresponded to evolving pulmonary infarcts on histopathology. Although retrospectively, the imaging findings were concordant with a spectrum of increasing severity of tumor embolization and vascular remodeling, the diagnosis of PTTM was not made premortem. PTTM is a rare entity that must be considered in cancer patients with unexplained hypoxemia, pulmonary hypertension and lung opacities on imaging.