Benign apocrine papillary lesions of the breast lacking or virtually lacking myoepithelial cells-potential pitfalls in diagnosing malignancy.

Two cases of apocrine papillary lesions are presented, in which myoepithelial cells were not visualized on hematoxylin and eosin-stained slides. A complex sclerosing papillary lesion did not exhibit myoepithelial cells on p63 and CD10 immunostaining, although a thin rim of myoepithelial cell cytoplasm was revealed by smooth muscle actin, calponin, and S100 immunostains. In the other lesion, without sclerosis, myoepithelium was not detected in the central papillary cores or at the periphery of the cystic wall on hematoxylin and eosin-stained sections or with any of the myoepithelial markers tested, although two small wall areas did display the presence of myoepithelium. These two cases strengthen the view that the lack of myoepithelium alone in apocrine lesions cannot be equated with malignancy. As recent literature reports have demonstrated that myoepithelial cells may be missing from benign apocrine changes and proliferations of different types, a reconsideration of the diagnostic criteria of the malignancy of such lesions appears essential.