Epithelioid-cell Myofibroblastoma of the Breast: Expanding the Morphologic Spectrum

Mammary Myofibroblastoma: Report of a Case and Review of the Literature

Mammary myofibroblastoma is a benign mesenchymal tumor composed of fibroblasts, myofibroblasts, and a variable number of adipocytes. Mammary myofibroblastoma usually occurs in men of older age and is less common in postmenopausal women. It may also happen in extramammary sites along the milk line. In this instance, it is referred to as mammary-type myofibroblastoma. Rarely multifocal and bilateral tumors have been described. Clinically and radiologically, it can be misinterpreted as a malignant tumor due to its rarity. Size usually does not exceed 3 cm. The diagnosis requires clinicopathological correlation with morphological and immunohistochemical evaluation, especially in limited biopsy specimens. We herewith describe a rare case of mammary myofibroblastoma in a 37-year-old female patient. We also review the literature focusing on the potential differential diagnostic issues and discuss this tumor's ultrastructural and cytogenetic findings.

Epithelioid myofibroblastoma of the breast: A case report and review of the literature

INTRODUCTION

Mammary myofibroblastoma (MFB) is a rare tumour. Its clinical and pathologic characteristics have been only sporadically described. A case of epithelioid variant of MFB is reported with the diagnostic tips, the differential diagnoses, and a discussion on the possible pathogenesis.

PRESENTATION OF CASE

A 74 year-old woman presented with a painless nodule in the left breast. Core needle biopsy (CNB) revealed a tumour primarily composed of epithelioid cells. Despite epithelioid appearance of the tumour cells, ductal/lobular components were absent within the tumour. As cell lineage of the epithelioid cells could not be determined with CNB, lumpectomy was performed to obtain definitive diagnosis and, at the same time, to remove the lesion. Histologically, the tumour consisted of multiple epithelioid cell nests that were spread over fibrous stroma infiltrated with adipose tissue. Spindle cells were also present, but they were fewer than epithelioid cell clusters. Occasionally, the tumour cells showed nuclear atypia. It was difficult to determine whether this tumour was benign or malignant solely with Hematoxylin-eosin stain. However, with the aid of immunohistochemical analyses, we could make a histodiagnosis of epithelioid subtype of myofibroblastoma.

DISCUSSION

The differential diagnoses of epithelioid MFB include ductal, lobular, metaplastic carcinomas and mesenchymal tumours. Comprehensive knowledge of classic and variant MFB is necessary for the correct diagnosis.

CONCLUSION

Pathologic diagnosis of epithelioid variant of MFB requires careful evaluation of histology and the use of a panel of immunohistochemistry. Female phenotype of breast stroma may play a role in the pathogenesis of MFB.

Myofibroblastoma of the Breast: Diagnosis, Pathology, and Management

Myofibroblastomas are rare benign spindle cell tumors that occur within both male and female breasts. They are composed of fibroblasts and myofibroblasts and are not associated with malignant potential. On mammographic and sonographic imaging, these tumors may present as oval circumscribed masses that overlap with the appearance of many benign entities, including fibroadenomas. Occasionally, the tumors may demonstrate interval growth or mimic imaging features of malignancy and require biopsy. Correct pathologic diagnosis is important because many morphologic variants exist, which complicates pathologic interpretation. The purpose of this article is to review the range of imaging manifestations and histopathological findings and to discuss current management.

Diagnostic challenges of intra-operative frozen consultation for mammary epithelioid myofibroblastoma

Myofibroblastoma (MFB) of the breast is a rare benign neoplasm that exhibits several morphologic variants and presents diagnostic challenges for pathologists, especially in recognizing intra-operative frozen sections. In order to raise awareness of this tumor and avoid misdiagnosis, we describe a case of a 38-year-old female patient diagnosed as epithelioid MFB. This painless tumor was well-circumscribed, found in the left breast and was physically examined over a period of six months. Histologically, this tumor was predominantly composed of epithelioid cells, which arranged as single cells, small clusters or nests. Tumor stroma was collagenized with spindle cells, adipose and focal myxoid areas. This case was misinterpreted as invasive carcinoma in the frozen section. The immunohistochemical profile demonstrated positivity for Vimentin, desmin, SMA, calponin, CD34, ER, PR and AR, whereas pan-keratin, keratin 7, keratin 34βE12, keratin 5/6, EMA, p63 and S100 were negative. RB1 was abnormally negative, confirming the diagnosis of epithelioid MFB. Making a correct diagnosis is primarily dependent on awareness by the pathologist of this unusual variant of MFB and careful integration of clinicopathologic findings to avoid potential diagnostic pitfalls.

PET/CT-Detected myofibroblastoma of the breast with bizarre cells: A potential diagnostic pitfall of malignancy

Myofibroblastoma (MFB) is a rare benign mesenchymal tumor usually occurring in the breast parenchyma. This tumor can present as a palpable nodule or can be incidentally detected as a nonpalpable mass on routine screening mammogram. We first report a rare case of histologically proven MFB of the breast revealed by fluoro‐deoxyglucose uptake on PET‐CT examination in a patient with a lung nodule. Tumor exhibited an unusual morphology, being predominantly composed of polygonal, epithelioid, and deciduoid‐like cells set in a myxoid stroma. The most striking feature was the multifocal presence of atypical/bizarre, mono/bi‐nucleated cells that, in addition to diffuse myxoid stromal changes, were a concern of malignancy, especially on core biopsy. The final diagnosis of MFB was achieved on surgically resected specimen and, similarly to other benign soft tissue tumors (especially leiomyoma and schwannoma/neurofibroma), the term “bizarre cell MFB of the breast” is proposed to emphasize the degenerative/reactive nature of the atypia.

A Rare Case of Epithelioid Myofibroblastoma of Breast Mimicking Lobular Carcinoma on Trucut Biopsy: a Diagnostic Pitfall and Literature Review

Epithelioid myofibroblastoma of the breast is a rare benign stromal tumor occurring in the postmenopausal females and elderly males. We report one such case in a 65-year-old female who underwent trucut biopsy from a well-defined right breast lump, which was misinterpreted as invasive lobular carcinoma on histology. Tumor showed mild to moderately pleomorphic tumor cells arranged in single file pattern, loosely dispersed and focally in sheets with inconspicuous nucleoli embedded in a fibrotic and hyalinized stroma. Immunohistochemistry for E-cadherin was negative further substantiating the morphological diagnosis. However, mastectomy specimen revealed it to be a case of epithelioid myofibroblastoma with the help of a large panel of immunohistochemical stains. In this report, we emphasize on the challenges of establishing this rare diagnosis mimicking lobular carcinoma, a diagnostic pitfall on trucut biopsy.

Clinicopathological and radiological characterization of myofibroblastoma of breast: A single institutional case review

Myofibroblastoma is a rare type of benign myofibroblastic neoplasm in the breast. It is clinically presented as a well-circumscribed mass, usually small in size (usually less than 4.0 cm), and can mostly be cured by local excision. Rare cases of giant myofibroblastoma greater than 10 cm have been reported, but also follow a benign clinical course. Histologically, breast myofibroblastoma is featured by bland fascicles of spindle cells intermixed with thick hyalinized collagen bundles. Mast cells are frequently found within the stroma. However, a wide spectrum of morphological variants can occur in myofibroblatoma, making its diagnosis challenging sometimes. Differential diagnosis of myofibroblastoma with other spindle cell lesions in the breast, either benign or malignant, is also important in practice. In this study, we collected 15 cases of breast myofibroblastoma diagnosed in our institution during a 20 year period. The sizes of these cases range from 0.4 cm to 35.2 cm (mean is 3.7 cm). To our knowledge, the case of giant breast myofibroblastoma we presented here is the largest one reported to date. The histological examination of the cases show great morphological variations. Besides the classical type, features of cellular, collagenized, palisading, epithelioid, myxoid, myoid, solitary fibrous tumor-like are also identified in the case series. Immunohistochemical staining patterns as well as clinical features of the cases are also summarized and compared. All cases in this study show no recurrence on follow-up. In addition, cases that are important differential diagnosis for breast myofibroblastoma are also studied. Their key histological characteristics are compared with myofibroblastoma, and their immunohistochemical and molecular features are discussed.

A novel collision tumour of myofibroblastoma and low-grade adenosquamous carcinoma in breast

BACKGROUND

Myofibroblastoma (MFB) and low-grade adenosquamous carcinoma (LGASC) are rare tumours in the breast, respectively. However, a collision tumour of the two types has never been reported.

CASE PRESENTATION

A 42-year-old female presented with a palpable mass in diameter of about 2.5 cm in the left breast. Morphologically, the lesion was predominately composed of bland spindle cells admixed with some islands of mature adipocytes and a few epithelial elements dispersing in infiltrating way which formed both tubule and solid structures. The mass showed low positive index of Ki-67. The spindle cells were strongly and diffusely positive for CD34, SMA, desmin, ER and PR. The epithelial elements were positive for CK and EMA, and negative for ER and PR completely. CK5/6 and P63 were positive in the outer-layer of the tubules and nearly all the cells of the solid nests.

CONCLUSIONS

A collision tumour of MFB and LGASC in breast is extremely rare and either component is supposed to be not overlooked. Excision and close follow-up are advised.

Rare Mesenchymal Breast Entities that Mimic Malignancy: A Single-institution Experience of a Challenging Diagnosis

Background

Benign mesenchymal tumors of the breast are rare and may mimic invasive carcinoma on imaging and morphology, thus becoming clinically challenging for clinicians, radiologists, and pathologists. To improve the understanding of these lesions and to avoid erroneous diagnosis and inappropriate treatment, we report our institution’s experience with seven cases of granular cell tumor (GCT) and myofibroblastoma (MFB) in the past 10 years.

Materials and methods

Seven cases of benign mesenchymal tumors of the breast were identified at the University of Texas Medical Branch from 2008 to 2018. Breast biopsies were collected from all patients after mammography and ultrasound imaging classified their results as suspicious or highly suggestive of malignancy by the Breast Imaging Reporting and Data System (BI-RADS ≥ 4A). All cases were reviewed to study the morphologic features and their immunoprofiles. The demographic characteristics, methods of treatment, postoperative pathological results, and follow-up results of the cases were then analyzed and compared to peer-reviewed literature.

Results

The study consisted of five females and two males with a mean age of 50 years in the GCT patients and 62 years in MFB patients. We identified four cases of GCT and three cases of MFB. The mean tumor size was 1.9 cm. Clinically, five patients presented with a palpable nontender mass, one with breast asymmetry, and one was asymptomatic. All patients underwent imaging studies prior to core needle biopsy. BI-RADS was ≥4B in patients with GCT and 4A-C in MFB. Definitive diagnosis was made by histopathology and confirmed by immunohistochemistry in accordance with the features described in the literature. Six patients underwent wide excision. The mean follow-up duration was 44.5 months. All patients remained well, without recurrence.

Conclusions

MFB and GCT can mimic malignant neoplasms and the clinical significance of these entities lies primarily in their recognition as distinctive benign neoplasms. The gold standard for the diagnosis of GCT and MFB is histopathology. All the cases in our series were clinically or radiologically mistaken for carcinoma, which has been largely reported in the literature. Pathologists should bear this in mind to avoid misdiagnosis and unnecessary treatment.

Utility of STAT6 and 13q14 deletion in the classification of the benign spindle cell stromal tumors of the breast

The boundaries of the benign spindle cell stromal tumors of the breast are still confusing. This is the reason why different names are interchangeably used for the same tumor and vice versa the same name for different tumors. Therefore, we studied the immunoexpression of easily available markers, such as CD34, α-smooth muscle actin, and desmin, with the addition of STAT6, as well as the chromosome 13q14 region by fluorescence in situ hybridization analysis in a series of 19 cases of benign spindle cell stromal tumors of the breast. Based on the morphologic and immunohistochemical findings, the following histotypes were identified: (i) tumors (10/19 cases) with the characteristic morphology of myofibroblastoma and stained with vimentin, CD34, desmin, and α-smooth muscle actin; (ii) fibroblastic benign spindle cell tumors (5/19 cases) composed of fibroblast-like cells stained only with vimentin and CD34; (iii) tumors (2/19 cases) with the typical morphologic features of solitary fibrous tumor and stained with vimentin, CD34, and STAT6; (iv) 1 case of spindle cell lipoma stained with vimentin and CD34; and (v) 1 case of fibroma composed of a paucicellular, diffusely hyalinized stroma with expression of vimentin and CD34. Notably most of the tumors, with the exception of solitary fibrous tumor, showed monoallelic deletion of FOXO1. This finding supports that myofibroblastoma, fibroblastic benign spindle cell tumor, spindle cell lipoma, and fibroma of the breast are histogenetically related lesions which belong to the same tumor entity.

Differential Diagnosis of Benign Spindle Cell Lesions

Spindle cell lesions of the breast cover a wide spectrum of diseases ranging from reactive tumor-like lesions to high-grade malignant tumors. The recognition of the benign spindle cell tumor-like lesions (nodular fasciitis; reactive spindle cell nodule after biopsy, inflammatory pseudotumor/inflammatory myofibroblastic tumor; fascicular variant of pseudoangiomatous stromal hyperplasia) and tumors (myofibroblastoma, benign fibroblastic spindle cell tumor, leiomyoma, schwannoma, spindle cell lipoma, solitary fibrous tumor, myxoma) is crucial to avoid confusion with morphologically similar but more aggressive bland-appearing spindle cell tumors, such as desmoid-type fibromatosis, low-grade (fibromatosis-like) spindle cell carcinoma, low-grade fibrosarcoma/myofibroblastic sarcoma and dermatofibrosarcoma protuberans.

Tumours composed of fat are no longer a simple diagnosis: an overview of fatty tumours with a spindle cell component

This is a review of the morphological spectrum of fatty tumours containing a component of spindle cells, highlighting the immunohistochemical and cytogenetic workup that is now mandatory for accurate diagnosis, with the goal of providing a practical approach for practising surgical pathologists. There have been significant advances in recent years in classifying and understanding the pathogenesis of fatty tumours with spindle cells, based on the correlation of histological, immunohistochemical and cytogenetic/molecular findings. In spite of this, morphological diagnosis and accurate classification of fatty tumours with spindle cells can be challenging to diagnostic pathologists. A group of three lesions: spindle cell lipoma, mammary-type myofibroblastoma and cellular angiofibroma share morphological features and are united by retinoblastoma protein (pRb) loss. Closely allied to these lesions, especially spindle cell lipoma is the newly designated atypical spindle cell lipomatous tumour, which shares morphological, immunohistochemical and cytogenetic features with the trio of tumours lacking nuclear pRb. All of these lesions lack MDM2 and CDK4 amplification as well and separation is based on clinical features, principally location. Atypical lipomatous tumour or well-differentiated liposarcoma shows retention of pRb but overexpression and amplification of MDM2. Fatty tumours with spindle cells need to be extensively sampled, with careful attention paid to cellular atypia and location, and they need to have immunohistochemical workup with pRb, MDM2, desmin, CD34 and p16. In addition, cytogenetic analysis for MDM2 and CDK4 amplification has become crucial for the proper identification of these lesions.

Lipomatous tumors of the breast: A contemporary review

Breast tumors with lipomatous or liposarcomatous components are infrequently encountered, but can be a source of diagnostic difficulty if the context of the fatty differentiation is not recognized. Among the true adipocytic tumors, lipoma is the most common lipomatous tumor arising in the breast. Several mammary spindle cell tumors may show adipocytic differentiation, including fibroepithelial tumors and myofibroblastoma. Liposarcomatous components most often arise in malignant phyllodes tumors, as opposed to primary liposarcomas of the breast which are believed to be uncommon. This article will review the spectrum fat-containing tumors of the breast with an emphasis on differential diagnosis and insights from recent molecular studies.

Myofibroblastic, fibroblastic and myoid lesions of the breast

Myofibroblastic, fibroblastic and/or myoid lesions are rare in the breast but comprise the majority of mammary mesenchymal spindle cell lesions. Whereas most have similar features to their counterparts at extramammary sites, pseudoangiomatous stromal hyperplasia is considered a breast-specific myofibroblastic proliferation on the same spectrum as myofibroblastoma. Other lesions with myofibroblastic/fibroblastic differentiation include fibromatosis and nodular fasciitis, as well as more aggressive tumors such as the rarely reported myofibrosarcoma, inflammatory myofibroblastic tumor and fibrosarcoma. Lesions with myoid differentiation include benign leiomyoma, myoid hamartoma and leiomyomatous myofibroblastoma, but primary leiomyosarcoma and rhabdomyosarcoma may also rarely arise in the breast. Furthermore, fibroepithelial lesions and metaplastic carcinomas can demonstrate myoid metaplasia. Diagnosis can be challenging, particularly on core biopsy, but benign lesions with or without recurrence potential must be distinguished from more aggressive tumors, especially metaplastic carcinoma and phyllodes tumors. This article will review lesions with myofibroblastic, fibroblastic and myoid differentiation in the breast, with special emphasis on differential diagnosis.

Myofibroblastoma

Myofibroblastoma of the breast is a rare benign mesenchymal tumor. We report a 61-year-old male case who presented to the orthopedic clinic with right shoulder pain. The physical and clinical examination was normal and he was referred to our clinic. Excision was performed and there were no postoperative complications.

Benign breast lesions that mimic malignancy

Many benign and reactive lesions of the breast show morphological overlap with malignant lesions. These benign mimics of malignancy often present diagnostic challenges to even the most experienced pathologists. This review focuses on several benign lesions of the breast that mimic malignant entities. For each of these lesions, we describe the key morphological and immunohistochemical features, potential diagnostic pitfalls, and our approach to arriving at the correct diagnosis.

Myofibroblastoma of the Breast: Literature Review and Case Report

Myofibroblastoma of the breast is a rare benign spindle cell tumor. The main aim of this study is to review the literature of this rare tumor. We present a case of a mammary myofibroblastoma occurring in an 82-year-old man, emphasizing the clinical, radiological, and pathological features. The tumor was successfully identified and managed in our hospital. We would like to draw the attention of clinicians to myofibroblastoma as a rare possibility in the differential diagnosis of a breast mass.

Epithelioid Myofibroblastoma of the Breast: A Report of Two Cases with Discussion of Diagnostic Pitfalls

Mesenchymal lesions of the breast are uncommon lesions which present diagnostic dilemmas for even the most experienced pathologists. Here, we present two cases of the epithelioid-variant of myofibroblastoma which were misdiagnosed as malignant lesions. Careful integration of clinical presentation, imaging, and close examination of the gross, histologic, and immunohistochemical findings can assist in differentiating these challenging lesions and avoiding diagnostic pitfalls.

Intraocular myofibroblastoma in an infant: a case report

BACKGROUND

Myofibroblastoma is a benign tumor composed of spindle cells and bands of hyalinized collagen. Intraocular myofibroblastoma in infancy is rarely encountered.

CASE PRESENTATION

The present study reports the case of a 4-month-old female baby with intraocular myofibroblastoma. She was suspected as corneal perforation due to the rupture of a corneal neoplasm in the right eye. The anterior segment was also involved according to the Color Doppler ultrasonography. A surgical exploration was performed and the protuberant part of the mass was resected. Conventional HE staining showed numerous spindle-shaped cells with bands of collagen beneath multilayers of well-differentiated corneal epithelia. Immunohistochemical staining demonstrated the tumor cells were strong positive for vimentin and smooth muscle actin, while negative for S-100 protein. The mass was confirmed as myofibroblastoma. After 12 month follow-up, there was no apparent growth of the tumor.

CONCLUSIONS

Myofibroblastoma is a very rare type of intraocular neoplasm, which may have complicated manifestation and could be misdiagnosed as dermoid or Peter's anomaly. Histopathological and immunohistochemical staining is crucial to form a precise diagnosis.

Epithelioid mammary myofibroblastoma mimicking invasive lobular carcinoma

A case of a 53-year-old woman with the epithelioid variant of mammary myofibroblastoma, which was initially misinterpreted as invasive lobular carcinoma, is presented. A needle core biopsy of the 1.6 cm mass showed interlacing bundles of epithelioid myofibroblasts amid dense fibrous tissue associated with lobular carcinoma in situ of the classical type. Most epithelioid cells showed nuclear atypia, and a few exhibited signet-ring cytology. Immunoreactivity for estrogen and progesterone receptors further compounded the deception, and the neoplasm was misinterpreted as invasive lobular carcinoma. Excisional biopsy showed a circumscribed stromal tumor with foci suspicious for invasive lobular carcinoma. The latter was excluded by cytokeratin negativity throughout the tumor. The overall histopathological appearance and immunostaining pattern was confirmatory of myofibroblastoma. This case report emphasizes the potential for mistaking epithelioid myofibroblastoma for invasive lobular carcinoma--particularly in the setting of limited sampling, hormone-receptor immunoreactivity of the lesional cells, and synchronous lobular carcinoma in situ.

Wilms' tumor protein (WT1) in mammary myofibroblastoma: an immunohistochemical study

Wilms' tumor protein (WT1) has been immunohistochemically detected in the cytoplasm of some developing, adult normal and neoplastic human tissues, suggesting its complex regulator activity in transcriptional/translational processes. Among neoplastic tissues, WT1 has been documented in the cytoplasm of benign and malignant vascular tumors and in rhabdomyosarcoma, while there are no available studies about its expression in myofibroblastic tumors. Accordingly, we studied immunohistochemically the potential expression of WT1 in mammary myofibroblastoma (MFB), a prototypical myofibroblastic tumor. A series of 18 cases of mammary MFB, including several morphological variants (classic, fibrotic, myxoid, lipomatous, Schwannian-like, and epithelioid variants), were tested with antibodies against the N-terminal of WT1. The most striking finding was a diffuse and strong WT1 cytoplasmic immunostaining restricted to the "epithelioid cell MFB", a rare and diagnostically challenging variant. Conversely the other variants of MFB, including the classic-type, were negative or only focally positive. The present study shows that mammary epithelioid cell MFB should be added to the list of mesenchymal tumors which express WT1 in the cytoplasm of neoplastic cells. Accordingly, we suggest that the detection of WT1 cytoplasmic immunoreactivity is of complementary diagnostic value to conventional myofibroblastic markers in identifying epithelioid cell myofibroblastoma.

Selected topics in the pathology of epithelioid soft tissue tumors

Epithelioid morphology, mimicking carcinoma, is a key or defining feature of several soft tissue tumors and may be seen in a wide variety of other tumors. This review will focus on those tumors defined at least in part by their epithelioid morphology, in particular epithelioid sarcoma, epithelioid malignant peripheral nerve sheath tumor, and sclerosing epithelioid fibrosarcoma. The role of loss of the SMARCB1 tumor-suppressor gene in the pathogenesis of these epithelioid soft tissue tumors will be discussed, as will their differential diagnosis with non-mesenchymal tumors, in particular carcinoma and melanoma.

Myofibroblastoma of the female breast with admixed but distinct foci of spindle cell lipoma: a case report

Mammary myofibroblastoma (MFB) is a rare benign spindle neoplasm that affects both sexes with a male predominance. It can exhibit a wide range of histological patterns. We report a case of epithelioid/spindle MFB of the female breast with admixed, but distinct, foci of spindle cell lipoma. Whilst all the spindle cells within the tumour expressed CD34, AR, ER, BCL2, and CD10, only those within the myofibroblastoma expressed desmin and only those within the lipomatous areas expressed S100. This finding, to our knowledge, is a novel one that has not been reported before.

From the radiologic pathology archives: diseases of the male breast: radiologic-pathologic correlation

Male breast disease includes a variety of benign and malignant conditions, many of which are hormonally influenced. Gynecomastia and skin lesions account for the majority of conditions in symptomatic men with a palpable abnormality, and these conditions should be accurately recognized. Imaging patterns of gynecomastia include nodular, dendritic, and diffuse patterns. Histopathologically, the nodular and dendritic patterns correlate with the florid and quiescent (fibrotic) phases of gynecomastia, respectively. The diffuse pattern may have features of both phases and is associated with exposure to exogenous estrogen. Benign-appearing palpable masses in male patients should be approached cautiously, given the overlapping morphologic features of benign and malignant tumors. In addition to gynecomastia, other benign male breast tumors include lipoma, pseudoangiomatous stromal hyperplasia, granular cell tumor, fibromatosis, myofibroblastoma, schwannoma, and hemangioma. Male breast cancer accounts for 1% of all breast carcinomas. Invasive ductal carcinoma accounts for the majority of cases in adult males and typically appears as a subareolar mass without calcifications that is eccentric to the nipple. Other epithelial and mesenchymal tumors that may occur, albeit not as commonly as in women, include papillary carcinoma, invasive lobular carcinoma, adenoid cystic carcinoma, liposarcoma, dermatofibrosarcoma, pleomorphic hyalinizing angiectatic tumor, basal cell carcinoma of the nipple, hematopoietic malignancies, and secondary tumors. Knowledge of the natural history, clinical characteristics, and imaging features of tumors that occur in the male breast will help narrow the radiologic differential diagnosis and optimize treatment.

Atypical epithelioid cell myofibroblastoma of the breast with multinodular growth pattern: a potential pitfall of malignancy

Myofibroblastoma (MFB) of the breast is the prototypical benign spindle cell tumor arising from the mammary stroma. Over the last two decades, several morphological variants of this tumor have been recognized. Epithelioid cell MFB is composed predominantly of neoplastic elements with epithelioid morphology. It represents a potential diagnostic pitfall of malignancy, especially when evaluating small biopsies. We report a unique case of a mammary epithelioid cell MFB composed of large mono- to multi-nucleated cells showing mild to moderate nuclear pleomorphism, predominantly arranged in a multinodular growth pattern. This tumor needs to be distinguished from invasive apocrine, oncocytic, pleomorphic lobular carcinoma, as well as metastases. Immunohistochemistry revealed the fibroblastic/myofibroblatic (positivity for vimentin, desmin, CD34 and focally for α-smooth muscle actin) nature of proliferating cells, and therefore was crucial for a correct diagnosis.

Myofibroblastoma of the Breast: Diagnostic Challenges of a Rare Benign Tumor

Breast myofibroblastomas (MFBs) are rare benign tumors that have recently been recognized as a distinct entity. They are more common in men and often coexist with gynecomastia. Fine needle aspiration cytology or core biopsy should always be performed for triple assessment; however, due to the multiple variants of the tumor, final diagnosis can be safely accomplished only postoperatively with the aid of immunohistochemistry. The main histological characteristic that differentiates MFBs from the majority of malignant mesenchymal breast lesions is the presence of spindle cells in a collagenous background. Low mitotic activity and vimentin and CD34 positivity have been reported as well. Surgical excision retains a pivotal diagnostic and curative role. Local resection is sufficient, but mastectomy can also be advocated either in cases of male patients with coexisting gynecomastia or in females with large tumors. Into this retrospective survey, three cases of breast MFB were consecutively enrolled. Two patients were postmenopausal females and one was male. Relevant literature is briefly reviewed. Clinical features, histogenesis, morphological, and immunochemical findings are discussed, while the role of the current diagnostic and therapeutic management of this uncommon neoplasm is emphasized.