Abstract
We describe a 68-year-old woman in whom screening mammography detected a mass classified as category 3. There was neither a palpable mass nor nipple discharge in the bilateral breasts on physical examination. Ultrasound showed a simple cyst. Eighteen months later, the patient noted the lump in the same area. Ultrasound showed a simple cyst that had enlarged to 12×9mm. Aspiration cytology was performed, and this yielded fluid stained with old blood. Cytology revealed class 2, and the cyst subsequently disappeared. Thirty months later, imaging studies showed a cluster of three simple cysts in the same location.Thereafter, the shape of the cyst changed, and it became palpable. As cytology showed class 5，excisional biopsy of the cyst was performed, and a diagnosis of ductal carcinoma in situ was established. The patient underwent wide excision with sentinel lymph node biopsy and irradiation (50Gy). Since then, she has continued endocrine therapy and there has been neither recurrence nor distant metastasis for five years. Intracystic carcinoma is a rare disease, accounting for 0.5～2.0% of all breast cancers. On the other hand, cysts are commonly encountered at breast clinics. If the lesion is diagnosed as a simple cyst without any symptoms, it is generally followed up. Cysts should be examined accurately and treated adequately because of the likelihood of intracystic carcinoma within the lesions, although the present case was considered to be extremely rare.
