Benign Smooth Muscle Cell Metaplasia in Breast

Unusual Myoid Differentiation in a Canine Benign Mixed Mammary Tumour

This report describes an unusual mesenchymal differentiation in a canine benign mixed mammary tumour. A 13-year-old crossbreed female dog was submitted to surgery to remove an inguinal mammary nodule. The tumour was composed of mammary epithelium and mesenchymal populations, not only of cartilage and bone but also of myoid cells. PTAH demonstrated cross striation of striated muscle, and immunohistochemistry highlighted striated muscle expressing desmin and calponin, and smooth muscle expressing desmin, SMA, and calponin. The tumour was diagnosed as a benign mixed tumour with leio- and rhabdomyoid differentiation. There was no tumour recurrence after one year of clinical follow-up. In conclusion, the well-differentiated features of leiomyocytes and rhabdomyocytes and the growth pattern define the benign origin of the mesenchymal component, which has been confirmed by a benign outcome; therefore, the knowledge of this kind of differentiation is helpful to avoid misdiagnoses.

Recurrent myoid hamartoma of the breast mimicking malignancy

Myoid (muscular) hamartoma is a rare form of benign breast hamartoma composed of differentiated mammary glandular and stromal structures, fatty tissue and areas of smooth muscle from which its name originates. It is considered to be a variant of a mammary hamartoma. We report the clinical presentation, imaging appearances and treatment of the initial and recurrent presentation of this rare tumour in a 61year old female, which mimicked malignancy.  Although rare, myoid hamartoma's can reoccur and when they do they imaging appearances of benign and malignant tumours can overlap tend to mimic malignancy and histological diagnosis is mandatory.

Evidence Supporting a Lymphatic Endothelium Origin for Angiomyolipoma, a TSC2(-) Tumor Related to Lymphangioleiomyomatosis

Angiomyolipoma (AML) is a tumor closely related to lymphangioleiomyomatosis (LAM). Both entities are characterized by the proliferation of smooth muscle actin and melanocytic glycoprotein 100 (recognized by antibody HMB-45)-positive spindle-shaped and epithelioid cells. AML and LAM are etiologically linked to mutations in the tsc2 and tsc1 genes in the case of LAM. These genes encode the proteins tuberous sclerosis complex (TSC)-1 and TSC2, which are directly involved in suppressing the mechanistic target of rapamycin cell growth signaling pathway. Although significant progress has been made in characterizing and pharmacologically slowing the progression of AML and LAM with rapamycin, our understanding of their pathogenesis lacks an identified cell of origin. We used an AML-derived cell line to determine whether TSC2 restitution brings about the cell type from which AML arises. We found that AML cells express lymphatic endothelial cell markers consistent with lymphatic endothelial cell precursors in vivo and in vitro. Moreover, on TSC2 correction, AML cells mature into adult lymphatic endothelial cells and have functional attributes characteristic of this cell lineage, suggesting a lymphatic endothelial cell of origin for AML. These effects are dependent on TSC2-mediated mechanistic target of rapamycin inactivation. Finally, we demonstrate the in vitro effectiveness of norcantharidin, a lymphangiogenesis inhibitor, as a potential co-adjuvant therapy in the treatment of AML.

Myoid hamartoma of the breast that proved difficult to diagnose: a case report

Myoid hamartomas of the breast are extremely rare breast lesions, with a poorly understood pathogenesis. We describe the case of a 38-year-old premenopausal woman who presenting with a mass in the left breast. Mammography revealed an oval mass that was partly indistinct, and ultrasonography showed a hypoechoic mass with a slightly irregular margin. Bilateral breast dynamic magnetic resonance imaging was performed for a more detailed evaluation. The images showed rapid initial enhancement and a microlobulated margin. Because the suspicion of malignancy was strong at that time, core needle biopsy was performed. Histologically, the tumor was identified as fibroadenoma. A case of myoid hamartoma of the breast that proved difficult to diagnose is reported, and discussed with reference to the literature.

Myoid hamartoma of the breast: a case report and review of the literature

Myoid hamartomas of the breast are extremely rare breast lesions, with a poorly understood pathogenesis. A 60-year-old woman presented with a palpable mass in the right breast. Breast ultrasonography and mammography showed the presence of a breast lesion with benign characters, but were not diagnostic. A local excision of the mass was performed; histology revealed that the tumor was composed of epithelial and stromal cells. Histological and immunohistochemical findings established the diagnosis of myoid hamartoma. The patient is well 4 years later without tumor recurrence. Breast myoid hamartomas are exceptionally rare benign lesions; complete surgical excision achieves cure.

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

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.

Muscular hamartoma of the breast. Case report and review of the literature

Muscular hamartoma (MH) is a rare tumor-like lesion of the breast, and only 22 cases have been reported in the literature. We report an additional case of MH of the breast, giving a new immunocytochemistry-based insight into the histogenesis of the smooth muscle component. The expression of CD34 antigen in smooth muscle cells suggested that MH originates from stromal cells via leiomyomatous metaplastic changes. This hypothesis was supported by the evidence that stromal cells in the normal parenchyma nearby the hamartoma were positive for CD34 antigen and, focally, also positive for smooth muscle markers (alpha-smooth muscle actin and desmin). A complete list of differential diagnoses and a review of the literature on the topic are provided. Although the use of the term "muscular hamartoma" could be considered inappropriate because of the absence of smooth muscle tissue in the normal breast, the authors underline that this designation can be easily accepted if the histogenesis of the heterologous component is regarded as a result of a stromal cell metaplastic change.

Epithelioid leiomyoma of the breast with granular cell change: a case report

A 42-year-old woman with an epithelioid granular cell leiomyoma of the right breast is reported. The cells were spindle to polygonal and displayed finely granular cytoplasm. The smooth muscle differentiation of this tumor was shown by the immunohistochemical positivity of the neoplastic cells with anti-alpha smooth actin and antidesmin antisera. Microfilaments with focal densities were present in the cytoplasm at an ultrastructural level. The granular cytoplasmic changes are related to a relevant number of lysosomes within the neoplastic cells.