Ewing sarcomas constitute a group of small, round, blue cell tumors of the bone and soft tissue. Extraskeletal Ewing sarcoma (EES) is a rare malignant neoplasm that arises from soft tissues, and it usually affects children and young adults. EES of the thoracopulmonary region commonly presents with a palpable mass or pain. Although rarely reported, EES affecting the anterior chest wall may present as a breast mass. We report a case of EES arising from the chest wall and manifesting as a palpable breast mass in a 22-year-old woman. The large mass was initially misdiagnosed as a breast origin mass on ultrasonography, but subsequent CT and MRI showed that the mass originated from the chest wall. Radiologists should be aware of the imaging findings of EES, and they should understand that chest wall lesions may be clinically confused as breast lesions.

Synovial sarcoma is a malignant soft tissue tumor that usually involves the extremities, particularly near the knees; a synovial sarcoma originating in the chest wall is extremely rare. We describe a 26-year-old woman diagnosed with a synovial sarcoma originating in the chest wall, based on CT and MRI findings. Contrast-enhanced CT images revealed a small, well-defined enhancing mass with calcification, in the subpleural area. This lesion was initially diagnosed as a benign tumor; however, the patient developed sudden severe pain with spontaneous bleeding and hemothorax, suggesting the possibility of malignancy. MRI revealed a multilobulated mass with a fluid-fluid level, which characterizes a synovial sarcoma.