Primary sarcomas of the breast are rare and constitute 0.6 to 1.2% of the total number of malignant tumours of the breast. A 42 years old housewife is admitted with a lump in her right breast. Examination revealed a 3 cm mobile cystic lump in the upper quadrant of her right breast. There were not palpable axillary nodes. Fibrocystic breast disease – macrocyst was considered after mammography and breast ultrasound. Fine needle aspiration biopsy was performed. It was determined 5 ml bloody fl uid on aspiration. Histologic examination was performed and this was reported as a malignant. Lumpectomy and axillary dissection were performed. The tumour was reported as a carcinosarcoma. She subsequently underwent adjuvant chemotherapy and radiotherapy because of breast-conserving surgery and size of the tumour. This report of a tumour in a young woman reinforces the surgical belief that any cystic lump including bloody fl uid should be adequately investigated to decide its nature.