Myoepithelial cells and basal lamina in poorly differentiated in situ ductcarcinoma of the breast - An immunocytochemical study

A retrospective study was made of 38 selected brest tumours with a poorly d ifferentiated in situ duct component. These were classified on haematoxylin and eosin (H&E) as ductal carcinoma in situ (DCIS; 10 cases), DCIS with in vasion (17 cases) and DCIS with features suggestive of for stromal invasion (11 cases). The last were these lesions composed of neoplastic ducts with irregular outlines and a myoepithelial layer that was not clearly evident o r large neoplastic ducts growing close together or surrounded by inflammato ry desmoplastic stroma. Cases of DCIS involving areas of sclerosing adenosi s were included in this category. Consecutive sections obtained from each c ase were studied with a panel of antibodies against myoepithelial cells (al pha smooth muscle actin and calponin) and basal lamina (BL) components (lam inin and type IV collagen). It was found that in situ lesions showed well-f ormed basal lamina and/or an evident myoepithelial layer. These features we re lacking in the invasive areas. Nine of the 11 cases with suggestive feat ures of stromal invasion were reclassified as invasive duct carcinoma (5 ca ses)and DCIS (4 cases), according to the absence or presence of a continuou s myoepithelial layer and/or basal lamina. In 2 such cases immunohistochemi stry yielded equivocal results and the label "suggestive of invasion" was t herefore pertinent. Immunohistochemistry facilitates the diagnosis of breas t DCIS; myoepithelial and basal lamina markers are useful in differentiatin g microinvasive from in situ ductal carcinomas of the breast.