Smooth muscle cell differentiation in mammary stromo-epithelial lesions with evidence of a dual origin: stromal myofibroblasts and myoepithelial cells

• Published in: Histopathology 2003-05, Vol.42 (5), p.448-456
• Main Authors: Di Tommaso, L, Pasquinelli, G, Damiani, S
• Format: Article
• Language: English
• Subjects: Adult; Aged; Aged, 80 and over; Biological and medical sciences; Biomarkers - analysis; breast; Breast Diseases - metabolism; Breast Diseases - pathology; Cell Differentiation; Cytoplasmic Structures - ultrastructure; Female; Fibroblasts - metabolism; Fibroblasts - pathology; Gynecology. Andrology. Obstetrics; hamartoma; Hamartoma - metabolism; Hamartoma - pathology; Humans; Immunohistochemistry; Mammary gland diseases; Medical sciences; Microscopy, Electron; Middle Aged; Muscle, Smooth - metabolism; Muscle, Smooth - pathology; Myocytes, Smooth Muscle - metabolism; Myocytes, Smooth Muscle - pathology; smooth muscle; Stromal Cells - metabolism; Stromal Cells - pathology; stromo-epithelial lesions; Tumors
• ISSN: 0309-0167; 1365-2559
• DOI: 10.1046/j.1365-2559.2003.01607.x

Aims:  We investigated the origin of myoid cells in benign stromo‐epithelial lesions of the breast in order to ascertain their myoepithelial or myofibroblastic origin. Methods and 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.