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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.

Adenolipomas are benign lesions characterised by an admixture of varying proportions of mature adipose tissue with normal glands. Only rare cases have been histologically documented in the breast (1), thyroid gland (2), parathyroid (3) and salivary gland (4). Recently Kunimura et al (5) described an adenolipoma of the colon. We report an additional case of adenolipoma of the colon in which the lipomatous component is characterised both by mature fat cells and by lipoblast-like cells.A 79 years old woman, treated for a colonic carcinoma in 1998, was found to have two polypoid lesions in the sigmoid colon. Endoscopically both lesions were peduncolated and reddish in colour and measured 6 and 10 mm, respectively, of greatest axis. They were resected and routinely processed for histological examination. At histology the smaller lesion was a tubular adenoma with mild dysplasia while the bigger one was characterised by the presence of tubular glands with focal mild dysplasia admixed with adipose tissue (Fig.1A), consistent with a diagnosis of adenolipoma. The adipose tissue was localised in the lamina propria in close relationship with the glands (Fig.1B) and was constituted mainly by mature fat cells and focally by lipoblast-like cells with the nucleus indented by multiple vacuoles (Fig.1C). The lipoblast-like cells were located at the periphery of an area with a reduction of glands and granulation tissue. Anti-S100 protein antibody stained both mature fat cells and lipoblast-like cells.Submucosal lipomas are not uncommon in the gastrointestinal tract, especially in the large bowel, and also rare cases of lipomatous polyposis have been described. However, in usual lipomas the glands are peripherally displaced by the adipose component and not intermingled with it. To the best of our knowledge, only a single case of adenolipoma of the colon has been previously reported (5). This was the case of a 50 years old man with a 11 mm polypoid lesion of the descending colon constituted by atypical tubular glands admixed with intramucosal mature fat cells. We report an additional case of adenolipoma of the colon characterised by mature fat cells and lipoblast-like cells. The latter were seen at the periphery of an area which probably underwent ulceration, thus they may represent a reactive change. This hypothesis was further supported by the clinical and endoscopic findings which ruled out any soft tissue tumour. Lipoblast-like cells have never been reported in adenolipomas of any site, nevertheless it has been suggested that brown fat cells of adenohibernoma might cause problems in the differential diagnosis with true lipoblasts (6).Adenolipomas of the colon are rare lesions, probably representing an analogue of adenolipoma of other organs, which can show reactive changes of their lipomatous component –i.e. lipoblast-like cells. Pathologists should be aware of this to avoid misdiagnosis of malignancy.

We investigated the origin of myoid cells in benign stromo-epithelial lesions of the breast in order to ascertain their myoepithelial or myofibroblastic origin.We selected 22 stromo-epithelial lesions of the breast and reviewed their morphological features at haematoxylin-eosin (HE) level. The lesions were classified as fibrous stromo-epithelial lesions (without evidence of myoid differentiation at HE 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.Myoid cell differentiation is common in stromo-epithelial lesions of the breast, and is evident in HE 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.