A 83-year-old female presented with a painful, palpable mass of the breast, which had been growing rapidly for the past few months. The physical examination revealed a 5×5 cm, elastic, hard, mobile mass with a smooth surface in the right breast. Ultrasound confirmed a 6×4 cm hypoechoic mass with regular borders in the inferior lateral quadrant of the right breast, which required core-needle biopsy to establish diagnosis. The histopathological result reported stromal neoplasm, suggestive of sarcoma or phyllodes tumor. CT scans of the chest and abdomen were negative for metastases. She underwent simple mastectomy and axillary node sampling. The postoperative course was uneventful, and she hoped no adjuvant therapies to be recommended. She is currently receiving outpatient follow-up care. Breast stromal sarcomas are rare and malignant tumors, hence, treatment protocols are not well-established. Early diagnosis of primary stromal sarcomas is essential, as they tend to spread very rapidly and are known to have poor prognosis.