We describe a case of pulmonary tumor embolism (PTE) from breast cancer diagnosed by selective aspiration cytology using a Swan-Ganz catheter. A 60-year-old woman was referred to Hamanomachi Hospital because of increased levels of tumor markers. The patient complained only of slight exertional dyspnea and a dry cough. Due to breast cancer, she had undergone a mastectomy followed by radiation and chemotherapy one year earlier. Positron emission tomography scanning with CT images revealed no evidence of malignancy. Repeated chest CT images showed emerging wedge-shaped nodules in the subpleural zones of the left lower lobe with diffuse ground-glass opacities in the bilateral lower lobes. The D-dimer level was negative. Pulmonary perfusion scintigraphy showed multiple small wedge-shaped defect areas on the peripheral sides of the bilateral lungs. Suspecting PTE, we performed selective aspiration cytology from the left pulmonary arteries. Cancer cells were detected from selected branches of left A8 and A9. Morphology and immunostaining led to a final diagnosis of PTE of recurrent breast cancer. Pulmonary embolism of cancer is a progressive, fatal condition with challenging diagnosis. Selective aspiration cytology with a Swan-Ganz catheter is a useful, less invasive option in patients with suspected PTE.