Intranuclear inclusions in epithelial cells of benign proliferative breast lesions.

Aim: To document and clarify the nature of intranuclear inclusions of luminal epithelium in benign proliferative breast lesions.
Methods and Results: Five benign breast lesions were selected which showed intranuclear inclusions within epithelial cells on light microscopy. Following confirmation of their luminal epithelial (non-myoepithelial) localisation by immunohistochemistry, ultrastructural examination was performed with the following observations: (1) presence of deep nuclear indentations occasionally verging on nuclear inclusions; (2) inclusions with features of helioid bodies; and (3) a morphological spectrum of helioid bodies and their focal coexistence.
Conclusion: Intranuclear inclusions of breast epithelium are likely of cytoplasmic origin. Helioid bodies may be formed by a stepwise process, the nature of which needs further study.