Smooth muscle cell differentiation in mammary stromo-epithelial lesions with evidence of a dual origin: stromal myofibroblasts and myoepithelial cells.
OBJECTIVE
We investigated the origin of myoid cells in benign stromo-epithelial lesions of the breast in order to ascertain their myoepithelial or myofibroblastic origin.


RESULTS
We selected 22 stromo-epithelial lesions of the breast and reviewed their morphological features at haematoxylin-eosin (H&E) level. The lesions were classified as fibrous stromo-epithelial lesions (without evidence of myoid differentiation at H&E level) (13 cases), type 1 myoid stromo-epithelial lesions (myoid cells directly merging with the myoepithelial layer) (three cases), type 2 myoid stromo-epithelial lesions (bundles of myoid cells unrelated to the glands) (six cases). All cases were studied immunohistochemically and myoid stromo-epithelial lesions were also studied with electron microscopy. The myoid component in two out of three cases of type 1 myoid lesions showed immunohistochemically co-expression of smooth muscle and myoepithelial markers. In contrast, the remainder showed immunohistochemical results identical to those found in type 2 myoid lesions (positivity with SMA, desmin, calponin, CD34 and bcl2 and negativity with cytokeratin 14 and p63). Ultrastructural study confirmed the presence of cells with myoepithelial features in type 1 myoid lesions and of cells with myofibroblastic features in type 2 myoid lesions.


CONCLUSIONS
Myoid cell differentiation is common in stromo-epithelial lesions of the breast, and is evident in H&E sections in up to 40% of cases. In addition, the origin of myoid cells is myofibroblastic in most cases, but in some cases, cells present immunohistochemical and ultrastructural evidence of myoepithelial origin.
Di Tommaso
L
L
Department of Oncologic Sciences, Bellaria Hospital, University of Bologna, Section of Anatomic Pathology, Italy.
Pasquinelli
G
G
Damiani
S
S
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000032:analysis; D001941:Breast Diseases / Q000378:metabolism / Q000473:pathology*; D002454:Cell Differentiation; D022083:Cytoplasmic Structures / Q000648:ultrastructure; D005260:Female; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology*; D006222:Hamartoma / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D008875:Middle Aged; D009130:Muscle, Smooth / Q000378:metabolism / Q000473:pathology*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism / Q000473:pathology*; D017154:Stromal Cells / Q000378:metabolism / Q000473:pathology*
D015415:Biomarkers