Is microglandular adenosis a precancerous disease? A study of carcinoma arising therein.

Microglandular adenosis (MGA) is a recently described and little appreciated proliferative glandular lesion of the breast that may mimic carcinoma both clinically and histologically. Several recent publications indicate that this lesion, while capable of recurrence if incompletely excised, is itself benign. In an earlier report from this institution we suggested that MGA might serve as the substrate for the development of mammary carcinoma. This report presents the pathologic findings in seven patients who developed carcinoma of the breast in association with MGA. The patients, aged 39-72, presented with firm masses that raised the clinical suspicion of carcinoma. The lesions reported here are linked not only by the presence of benign MGA associated with mammary carcinoma, but by a spectrum of atypical glandular proliferations ("atypical" MGA) that suggest transitions from MGA to infiltrating carcinoma. These carcinomas shared unusual histologic features which strengthen our impression that they are derived from MGA. On the basis of the experience presented in this study, it appears that MGA may on occasion serve as the substrate for the development of mammary carcinoma. For patients with uncomplicated MGA, complete excision of the lesion with clinical follow-up is recommended. When atypical hyperplasia is present in MGA, the lesion should be widely excised and the same caution exercised in following the patient as with other atypical hyperplasias. The treatment of carcinoma arising in MGA will depend on the stage of the disease. Presently we do not know whether these carcinomas have unusual clinical or biological characteristics.