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.