Cystic carcinoma of the breast: a trap for the unwary.

Cystic breast masses are a common presentation to breast clinics. While the majority of cysts can be managed by simple aspiration, a small proportion are malignant. Histology records for a 10-year period have been examined to identify patients with cystic breast carcinomas. In all, 31 patients were identified. Of these, 18 had cystic degeneration of high-grade tumours, while 13 had intracystic papillary carcinoma. Both of these tumour types were diagnosed by a combination of cyst fluid cytology and breast imaging. The prognosis of high-grade tumours was poor, while that of intracystic papillary carcinomas was excellent. After cyst aspiration, bloodstained fluid should be sent for cytology and breast imaging arranged in all patients. Patients in whom a cyst refills within 2 week of aspiration require a careful re-evaluation. Cysts in postmenopausal women should be viewed with suspicion. Excision should be performed in patients with positive cytology or imaging.