Conventional histology and immunostaining of two malignant adenomyoepitheliomas of the breast. A, C and E shows a biphasic malignant adenomyoepithelial tumour with distinct tubular formations, whereas B, D and F show a monophasic adenomyoepithelial carcinoma with diffuse infiltration of adipose tissue.(H&E, magnification ×20 C and D display distribution patterns of basal cytokeratin expression that are tantamount to the proportion of tumour cells (immunostaining for Ck5/6, magnification ×20). E and F show expression of SMA in a more irregular distribution compared to normal breast tissue in the malignant biphasic lesion and a rather diffuse pattern in monophasic lesions. A prominent mitotic figure is marked in F (arrow) (magnification ×20).