In situ lobular neoplasia of the breast with marked myoepithelial proliferation.

AIMS

To present four new cases of in situ lobular neoplasia associated with marked proliferation of myoepithelial cells.

METHODS AND RESULTS

Four recently seen cases showing extensive foci of in situ lobular neoplasia, as confirmed by negative E-cadherin staining, were stained for myoepithelial cells using CD10, smooth muscle actin and cytokeratin 5/6. Invasive lobular carcinoma was also present in two cases; one case was associated with multiple foci of collagenous spherulosis, and one was associated with a radial scar. Marked myoepithelial proliferation was seen around most of the in situ lobular foci or mingled with lobular cells.

CONCLUSIONS

Marked proliferation of myoepithelial cells is sometimes encountered in association with extensive in situ lobular neoplasia. It is suggested that this proliferation might have a role in maintaining the in situ status of these lesions or, alternatively, that there is a shared factor responsible for the simultaneous proliferation of certain 'lobular' cell types and myoepithelial cells.