The relationship of cyst type to risk factors for breast cancer and the subsequent development of breast cancer in patients with breast cystic disease.

The frequency of epithelial hyperplasia and papillary apocrine change in patients with palpable breast cysts lined by either apocrine or flattened epithelium has been compared. Hyperplasia of any degree, severe hyperplasia with or without atypia and papillary apocrine change were all seen significantly more frequently in patients with clinically palpable apocrine cysts. Twelve patients were identified with breast cancer with a history of cyst aspiration, in whom all cysts aspirated could be classified as apocrine or flattened on the basis of cytology or electrolyte composition of cyst fluid. Eleven patients had single or multiple apocrine cysts and one had a single flattened cyst. This represents a significantly increased preponderance of apocrine cysts as compared with that normally seen in patients with cystic disease. The mastectomy specimens of those 11 patients with a history of apocrine cyst aspiration more frequently contained hyperplastic changes and non-invasive carcinoma than age- and menopausal-matched controls who did not have a history of cystic disease. This study suggests that patients who develop cysts lined by apocrine epithelium may be at a greater risk of subsequent breast cancer than those with flattened epithelial cysts.