Acidophilic nuclear inclusions are specific for florid ductal hyperplasia among proliferative breast lesions

Context.-Recently we have observed distinctive acidophilic intranuclear inclusions in cases of usual intraductal hyperplasia of the breast. Similar inclusions were described almost 20 years ago in cases of mammary hyperplasia. These correlated ultrastructurally with so-called helioid inclusions. However, there since has been little discussion of these inclusions in the literature. Objective.-To examine the incidence and specificity of these inclusions in proliferative lesions of the breast. Design.-Forty cases of usual intraductal hyperplasia, 15 cases of atypical ductal hyperplasia, and 34 cases of lowgrade ductal carcinoma in situ were examined for the presence of acidophilic intranuclear inclusions. Results.-Acidophilic intranuclear inclusions were present in 50% of cases of usual intraductal hyperplasia (20 of 40) but were not identified in any cases of atypical ductal hyperplasia (0 of 15) or low-grade ductal carcinoma in situ (0 of 34). Conclusions.-Acidophilic intranuclear inclusions appear to be a common, specific feature found in usual intraductal hyperplasia and may be helpful in distinguishing it from atypical ductal hyperplasia and low-grade ductal carcinoma in situ in some cases. Elucidating the nature of these inclusions may provide insight into the pathogenesis of usual intraductal hyperplasia.