Myofibrosarcoma of the upper jawbones: a clinicopathologic and ultrastructural study of two cases

Low-grade myofibrosarcoma of the maxillary sinus: Two case reports

BACKGROUND

Low-grade myofibroblastic sarcoma (LGMS) is an extremely rare tumor characterized by the malignant proliferation of myofibroblasts. LGMS most commonly develops in adults, predominantly in males, in the head and neck region, oral cavity, especially on the tongue, mandible, and larynx. This article presents 2 cases of LGMS localized to the maxillary sinus and provides an overview of the available literature.

CASE SUMMARY

Two patients with LGMS located in the maxillary sinus underwent surgery at the Department of Head and Neck Surgery. Case 1: A 46-year-old patient was admitted to the clinic with suspected LGMS recurrence in the right maxillary sinus (rT4aN0M0), with symptoms of pain in the suborbital area, watering of the right eye, thick discharge from the right nostril, and augmented facial asymmetry. After open biopsy-confirmed LGMS, the patient underwent expanded maxillectomy of the right side with immediate palate reconstruction using a microvascular skin flap harvested surgically from the middle arm. The patient qualified for adjuvant radiotherapy for the postoperative bed, with an additional margin. Currently, the patient is under 1.5 years of observation with no evidence of disease. Case 2: A 45-year-old man was admitted to our clinic with facial asymmetry, strabismus, exophthalmos, and visual impairment in the right eye. Six months earlier, the patient had undergone partial jaw resection at another hospital for fibromatosis. A contrast-enhanced computed tomography scan revealed a tumor mass in the postoperative log after an earlier procedure. An open biopsy confirmed low-grade fibrosarcoma (rT4aN0M0). The patient qualified for an extended total right maxillectomy with orbital excision and right hemimandibulectomy with immediate microvascular reconstruction using an anterolateral thigh flap. The patient subsequently underwent adjuvant radiotherapy to the postoperative area. After 9 months, recurrence occurred in the right mandibular arch below the irradiated area. The lesion infiltrated the base of the skull, which warranted the withdrawal of radiotherapy and salvage surgery. The patient qualified for palliative chemotherapy with a regimen of doxorubicin + dacarbazine + cyclophosphamide and palliative radiotherapy for bone metastases. The patient died 26 months after surgical treatment. The cases have been assessed and compared with cases in the literature.

CONCLUSION

No specific diagnostic criteria or treatment strategies have been developed for LGMS. The treatment used for LGMS is the same as that used for sinonasal cancer radical tumor excision; adjuvant radiotherapy or chemoradiotherapy should also be considered. They have low malignant potential but are highly invasive, tend to recur, and metastasize to distant sites. Patients should undergo regular follow-up examinations to detect recurrence or metastasis at an early stage. Patients should be treated and observed at the highest referral centers.

Low-Grade Myofibroblastic Sarcoma of the Oral and Maxillofacial Region: An International Clinicopathologic Study of 13 Cases and Literature Review

Low-grade myofibroblastic sarcoma (LGMS) represents an atypical tumor composed of myofibroblasts with a variety of histological patterns and with a high tendency to local recurrence and a low probability of distant metastases. LGMS has predilection for the head and neck regions, especially the oral cavity. This study aimed to report 13 new cases of LGMS arising in the oral and maxillofacial region. This study included LGMS cases from five oral and maxillofacial pathology laboratories in four different countries (Brazil, Peru, Guatemala, and South Africa). Their clinical, radiographic, histopathological, and immunohistochemical findings were evaluated. In this current international case series, most patients were females with a mean age of 38.7 years, and commonly presenting a nodular lesion in maxilla. Microscopically, all cases showed a neoplasm formed by oval to spindle cells in a fibrous stroma with myxoid and dense areas, some atypical mitoses, and prominent nucleoli. The immunohistochemical panel showed positivity for smooth muscle actin (12 of 13 cases), HHF35 (2 of 4 cases), β-catenin (3 of 5 cases), desmin (3 of 11 cases), and Ki-67 (range from 5 to 50%). H-caldesmon was negative for all cases. The diagnosis of LGMS was confirmed in all cases. LGMS shows predominance in young adults, with a slight predilection for the female sex, and maxillary region. LGMS should be a differential diagnosis of myofibroblastic lesions that show a proliferation of spindle cells in a fibrous stroma with myxoid and dense areas and some atypical mitoses, supporting the diagnosis with a complementary immunohistochemical study. Complete surgical excision with clear margins is the treatment of choice. However, long-term follow-up information is required before definitive conclusions can be drawn regarding the incidence of recurrence and the possibility of metastasis.

Risk Factors for Recurrence and the Role of Radiotherapy in Low-grade Myofibroblastic Sarcoma: A Systematic Review

Low-grade myofibroblastic sarcoma (LGMS) is a rare malignancy that commonly occurs in the head and neck region. The role of radiotherapy has been unclear in treating LGMS and the risk factors for recurrence have remained undefined. The objective of this study is to determine risk factors for the recurrence of LGMS in the head and neck as well as the role of radiotherapy in the treatment of LGMS. A comprehensive review of the literature was performed through Pubmed leading to the inclusion of 36 articles after our inclusion and exclusion criteria were applied. Continuous variables were analyzed with a 2-tail unpaired t test. Categorical variables were assessed with the χ 2 test or Fisher exact test. Logistic regression and multivariable logistic regression analysis with 95% CIs were used to obtain odds ratios. LGMS most commonly occurred in the oral cavity (49.2%). Half of all recurrences occurred in the paranasal sinuses/skull base. LGMS occurring at the paranasal sinuses/skull base had a significantly increased risk of recurrence compared with other subsites within the head and neck (odds ratio: -40; 95% CI: 2.190, 762.005; P = 0.013). The average time to recurrence of LGMS was 19.2 months. Adjuvant treatment with radiation did not improve recurrence rates. Sex, tumor size, or bony involvement were not found as risk factors for recurrence. Patients with LGMS of the paranasal sinuses and skull base are at high risk for recurrence and should be monitored closely. The role of adjuvant radiation treatment in these patients remains unclear.

The clinical challenges and dilemma in the management of uncommon maxillary sinus tumors - A report of two cases

Maxillary sinus is the common site for the nose and paranasal sinus tumors with diverse histopathological types and the treatment for each may differ. Making a histopathological diagnosis on occasion can be challenging. We had two patients presenting with upper alveolus growth in whom establishing the histopathological diagnosis was challenging. Through clinical evaluation, imaging (computed tomography and/or magnetic resonance imaging) and identification of key histopathological features helped in the management of these patients.

Low-grade myofibroblastic sarcoma of the orbit: A case report and literature review

RATIONALE

Low-grade myofibroblastic sarcoma (LGMS) is a malignant lesion composed of myofibroblasts. It is an uncommon tumor of unknown etiology that mainly develops in the bone or soft tissue and is most often reported in the head and neck, particularly in the tongue and oral cavity.

PATIENT CONCERNS

A 2-year-old girl, previously well and with no significant medical history or family history of other diseases, presented with a 2-week painless swelling of the right orbit.

DIAGNOSES

Preoperative computed tomography (CT) revealed a large homogeneous enhanced mass, 21 × 13 mm in size, located on lateral wall of the right orbit with bone absorption. The mass was resected and histopathological examination revealed LGMS of the orbit.

INTERVENTIONS

On May 2016, she underwent surgery without the additional postoperative treatment.

OUTCOMES

The patient's postoperative course was uneventful, and was discharged on the 6th day after surgery. During a year follow-up period, there was no recurrence of the postoperative CT. The patient and her family were satisfied with the result of the surgery.

LESSONS

Based on clinical characteristics and postoperative CT, we considered the mass may be a benign tumor. We completely resected along the capsule without an extensive surgical margin. However, postoperative histopathology diagnose LGMS, which shows a strong potential for local recurrence and vascular invasion. So we should close observation of the patient's symptoms and sign. If the tumor has invaded adjacent tissues, we will use adjuvant chemotherapy or radiotherapy.

Indolent growth of low-grade myofibroblastic sarcoma of the cheek mimics benign lesions: A case report and literature review

Low-grade myofibroblastic sarcoma (LGMS) is a neoplasm of the soft tissue characterized by myofibroblastic differentiation. This type of tumor has been observed in various sites in the whole body, but frequently occurs in the head and neck region. It typically presents as a slow-growing painless mass, which is often mistaken for a benign lesion due to its indolent growth; however, LGMS is a malignant neoplasm. In the present study, a 43-year-old female presented with a 14-mm LGMS lesion in the buccal subcutaneous tissues of the buccinator muscle. The patient had initially noticed the lesion 2-months prior to presenting at the hospital. Following biopsy, the tumor was surgically resected and no recurrence or metastasis was observed during a follow-up time of 2 years. To the best of our knowledge, this case is the first report of LGMS located in the buccal subcutaneous tissue of the buccinator muscle. The present study a literature review of 55 cases of this tumor type in the head and neck region was conducted, revealing that the indolent growth of these lesions may contribute to a delay in diagnosis. The average time between the onset of clinical symptoms and hospital admission is 3.9 months, and this form of tumor is frequently misdiagnosed as a benign lesion. Therefore, the present study suggests that an incisional biopsy may be performed to rule out LGMS when clinicians encounter patients with the aforementioned indolent lesions anywhere in the body. In addition, the avoidance of radiotherapy is recommended following resection of the LGMS tumor, as it may induce LGMS recurrence.

Low-grade myofibroblastic sarcoma of the palate

Low-grade myofibroblastic sarcoma (LGMS) is a rare, malignant tumor with myofibroblastic differentiation. Despite it being classified as a distinct entity by the World Health Organization, a few cases were reported in the oral and maxillofacial region. Here, a LGMS developed on the palate of a 73-year-old man who presented with a 1-cm tumor on the posterior border of the palate. Based on the histological and immunohistochemical features, a diagnosis of LGMS was established. The tumor was resected, and no recurrence was observed over 2 years. Although the tongue is the most preferred site for LGMS, it may occur in any region of the oral cavity.

Low-grade myofibroblastic sarcoma of the larynx

Low-grade myofibroblastic sarcoma is an uncommon sarcoma with myofibroblastic differentiation. It occurs in a wide variety of sites and has a predilection for the head and neck region. Biologically, low-grade myofibroblastic sarcoma has a propensity for local recurrence and is associated with a low risk of metastatic spread. Histologically, it can mimic a variety of different types of benign and malignant processes and often requires immunohistochemical analysis for its accurate identification. This report describes a case and discusses the differential diagnosis of a low-grade myofibroblastic sarcoma that arose in the larynx of a 69-year-old woman with a history of metastatic skin melanoma. To the best of the authors' knowledge this is the first description in the English literature of low-grade myofibroblastic sarcoma originating in the larynx.

Low-grade myofibroblastic sarcoma of the sacrum

Myofibroblastic tumors are soft-tissue neoplasms arising from myofibroblasts, ubiquitous cells sharing ultrastructural features of muscular and fibroblastic cells. Vasudev and Harris described a malignant counterpart of these benign tumors in 1978. Most reported cases of myofibroblastic sarcoma have arisen in the head and neck region and the soft tissues of the extremities. To the best of the authors' knowledge, there have been only 8 previous reports on primary myofibroblastic sarcoma of the bone. The authors report a new case of this rare tumor affecting the sacrum and ilium of a 15-year-old girl and discuss the role of total sacrectomy and lumbopelvic reconstruction for treatment of this disease.

A rare case of low-grade myofibroblastic sarcoma of the femur in a 38-year-old woman: a case report

Introduction

Primary myofibroblastic sarcoma of the bone is a rare spindle cell tumour with, to the best of our knowledge, only eight cases reported in the available English language literature. The disease's rarity and its low-grade features make an accurate diagnosis difficult in most cases. The differential diagnoses of this unusual tumour include various benign entities as well as other sarcomas. Due to the difference in prognosis, a precise pathologic diagnosis is essential, which requires a combination of thorough morphologic examination, immunohistochemistry and electron microscopy wherever available.

Case presentation

We report the case of a 38-year-old Indian woman with a lytic lesion in her left femur. The tumour was associated with cortical destruction and soft tissue extension. A biopsy from the soft tissue component showed features suggestive of a low-grade malignant mesenchymal tumour. Excision of the tumour was performed and histopathological examination showed a low-grade spindle cell sarcoma with collagenous stroma. Expressions of vimentin and smooth muscle actin were also noted. Ultrastructural examination confirmed its myofibroblastic nature. A final diagnosis of low-grade myofibroblastic sarcoma of the left femur was thus rendered.

Conclusion

Low-grade myofibroblastic sarcoma is one of the rarer osseous spindle cell sarcomas depicting a favourable prognosis in the cases reported so far. Its diagnosis requires ancillary techniques like immunohistochemistry and electron microscopy. To the best of our knowledge, we report the ninth case in the literature and the first case from our subcontinent.

Low-grade myofibroblastic sarcoma of the oral cavity

Two cases of low-grade myofibroblastic sarcoma (LGMS) are presented: one of lateral tongue, the other of lower buccal vestibule. LGMS represents a distinct atypical myofibroblastic tumor that occurs in several sites, primarily within the head and neck regions. A painless, enlarging mass is the most common clinical presentation, but a definitive diagnosis requires both histopathological and immunohistochemical analyses. Histologically, LGMS commonly presents as a cellular lesion composed of spindle-shaped tumor cells arranged primarily in fascicles with a diffusely infiltrative pattern. Immunohistochemically, LGMS shows positive staining for at least one myogenic marker, such as desmin, and muscle actin.

Myofibroblastic sarcoma vs nodular fasciitis: a comparative study of chromosomal imbalances

We investigated the molecular cytogenetic features in myofibroblastic sarcoma (MS) to gain insight into the nature of the controversial entity. DNA copy number changes were analyzed by comparative genomic hybridization in 29 cases of MS and 5 cases of nodular fasciitis. The characteristic chromosomal imbalances in MS were gains at 1p11 --> p36.3 (19/29 [66%]), 12p12.2 --> p13.2 (13/29 [45%]), 5p13.2 --> p15.3 (9/29 [31%]), and chromosome 22 (8/29 [28%]) and loss at 15q25 --> q26.2 (7/29 [24%]). In contrast, only 1 of 5 cases of nodular fasciitis showed genetic aberrations. The average number of aberrations in nodular fasciitis (0.4) was significantly lower than that in MS (5.4). Thus, MS displayed complex DNA copy number changes and shared no range of common chromosomal abnormality with nodular fasciitis, indicating that distinct genetic pathways may be involved in the development of these entities.

Low-grade myofibroblastic sarcoma of the tongue

Low-grade myofibroblastic sarcoma is a neoplasm of atypical myofibroblasts with fibromatoseslike features and a predilection for head and neck sites, including the oral cavity. These lesions have only been characterized in the last 2 decades, and controversies in the concept of neoplastic myofibroblasts still exist. Lack of obvious cytological atypia may result in their being mistaken for reactive fascitislike lesions or fibromatosis and architectural similarities to fibrosarcoma or leiomyosarcoma may complicate the diagnostic process. This paper describes a spindle cell neoplasm in a 40-year-old man that was diagnosed 9 years ago as an unclassifiable myofibroblastic proliferation. The recurrent tumor, which presented 6 years following excision of the original tumor, was subsequently classified as a low-grade myofibroblastic sarcoma. The morphological, immunohistochemical, and electron microscopic features of this unusual sarcoma and the most likely differential diagnoses are discussed.

Myofibroblastic sarcoma of the nasal cavity and paranasal sinus: a clinicopathologic study of 6 cases and review of the literature

OBJECTIVE

We describe the clinicopathologic features of 6 cases of myofibroblastic sarcoma (MS) occurring in the nasal cavity and paranasal sinus.

STUDY DESIGN

The paraffin-embedded tissues of 6 cases of MS were stained immunohistochemically and examined by electron microscopy.

RESULTS

Clinically, a painless enlarging mass was the most common symptom, followed by the nasal obstruction, epistaxis, copious rhinorrhea, and proptosis. Histologically, the tumors showed a diffusely infiltrative growth pattern and consisted mainly of spindle cells with abundant eosinophilic cytoplasm. The hypocellular myxoid areas and the hypercellular fibrous areas were identified. Immunohistochemically, all 6 tumors were positive for vimentin, alpha-smooth muscle actin, calponin, and fibronectin. Ultrastructural examination in 3 cases showed characteristic features of myofibroblast. Follow-up in 6 patients revealed high local recurrence rate (6 out of 6).

CONCLUSION

Myofibroblastic sarcoma of the nasal cavity and paranasal sinus exhibit diverse histologic appearances and a strong aggressive behavior.

Cutaneous mixed tumor with lipomatous stroma

AIM

Mixed tumors are usually composed of two components, one epithelial and the other mesenchymal. The latter component is commonly myxoid or myxochondroid; a massively lipomatous stroma is very unusual. To date, only two cases of mixed tumor of the skin have been reported with this type of stroma.

METHODS AND RESULTS

We report the case of a 61-year-old man with a mixed tumor situated on the hand, an unusual site for these tumors, with over 90% of the tumor composed of adipose tissue. The tumor was a well-circumscribed, 4.5-cm mass, with the gross appearance of a lipoma. The lipomatous stroma contained nests and ribbons of epithelial cells, with occasional tubular structures, surrounded by a scarce amount of fibromyxoid tissue. Immunohistochemical study showed findings similar to those seen in classic mixed tumors.

CONCLUSION

Together with a few other cases in the skin and parotid gland, this report shows how massive adipose differentiation can arise in a mixed tumor of the skin.

Low-grade myofibroblastic sarcoma of the piriform fossa: a case report with a literature review of a tumour with a predilection for the head and neck

A low-grade myofibroblastic sarcoma was removed from the pyriform fossa of a 44-year-old man. It recurred 4 years later and was removed radically through an incision in the neck. There has been no further recurrence after 11 years.

Myofibrosarcoma of the nasal bone

Myofibrosarcoma is a recently recognized rare tumor that mainly occurs in adults. These tumors are composed of a collagenous stroma and pleomorphic stellate to spindle-shaped cells that resemble smooth muscle cells with eosinophilic cytoplasm and tapered nuclei. We present a case of myofibrosarcoma of the nasal bones in a 4-year-old girl who showed rapid enlargement of a painless glabellar swelling. Computed tomography and magnetic resonance imaging revealed an expanding solid mass with erosion of the surrounding nasal bones. After excision and histopathological examination, this tumor was identified as a myofibrosarcoma. This is the first report of such a tumor localized to the glabellar region. This case report contributes to better awareness of an extremely rare type of glabellar lesion in children.

Low-grade sarcomas with CD34-positive fibroblasts and low-grade myofibroblastic sarcomas

A subset of low-grade fibrosarcomas is composed of CD34-positive spindle cells. These include dermatofibrosarcoma, its morphologic variants, and its associated fibrosarcoma, solitary fibrous tumor, hemangiopericytoma and their malignant counterparts, and some cases of myxoinflammatory fibroblastic sarcoma. Dermatofibrosarcoma and related lesions are characterized by a t(17;22)(q22;q13) rearrangement resulting in fusion of the genes COL1A (17q21-22) and PDGFB1 (22q13). Solitary fibrous tumor displays varying cellularity and fibrosis and a peripheral hemangiopericytomatous pattern; most tumors formerly called hemangiopericytoma are now subsumed into the category of solitary fibrous tumor, although a few strictly defined examples are recognized; however, these are probably not composed of pericytes. Myofibroblastic malignancies are best identified by electron microscopy, with which varying degrees of differentiation, including the presence of fibronexus junctions, can be identified. Low-grade sarcomas showing myofibroblastic differentiation include myofibrosarcomas and inflammatory myofibroblastic tumors. Myofibrosarcomas are spindle cell neoplasms that occur in children or adults in the head and neck, trunk, and extremities as infiltrative neoplasms and that display a fascicular or fasciitis-like pattern with focal nuclear atypia and variable expression of myoid antigens. These sarcomas are prone to recurrence and a small number metastasize. Inflammatory myofibroblastic tumor (synonymous with inflammatory fibrosarcoma) is a neoplasm arising predominantly in childhood, and frequently in intraabdominal locations. It has spindle cells in fascicular, fasciitis-like and sclerosing patterns, with heavy chronic inflammation including abundant plasma cells. Many IMT have clonal chromosomal abnormalities involving 2p22-24, and fusion of the ALK gene with tropomyosin 3 (TPM3-ALK) or tropomyosin 4 (TPM4-ALK) is found in a subset.

Desmoplastic fibroblastoma: a light and ultrastructural description of two cases

The authors report 2 cases of collagenous fibroma in which ultrastructural analysis revealed the presence of fibronexus junctions, markers of myofibroblastic differentiation, never described in this rare lesion before. The tumors occurred in the trapezius muscle and in the right arms of a 41 -year-old and a 25-year-old man. They were both intramuscular and showed sharp edges. Grossly, the excised masses were whitish and firm. Microscopically, they were both composed of stellate or spindle-shaped cells separated by a collagenous hypovascular and focally myxoid stroma. Mitotic figures and necrotic areas were not identified. Immunohistochemistry showed positivity for vimentin and focal positivity for smooth and human muscle actin, and flow cytometry showed the tumoral cells to be diploid.

Myofibroblastic malignancies

Malignant tumors composed of myofibroblasts are increasingly being recognized, but their existence remains controversial. Currently accepted examples within this category represent spindle cell or pleomorphic neoplasms of the soft tissues with a spectrum of histological grades. Low- and intermediate-grade myofibrosarcomas are fascicular spindle cell neoplasms resembling fibrosarcoma or leiomyosarcoma. They infiltrate deep soft tissue with disproportionate involvement of head and neck sites and can recur locally but infrequently metastasize. They variably express myoid immunohistochemical markers, and their differential diagnosis includes benign myofibroblastic proliferations such as fasciitis and fibromatosis as well as other types of spindle cell sarcoma. High-grade (pleomorphic) myofibrosarcomas are an ultrastructurally defined subset of malignant fibrous histiocytoma, which they resemble in morphology and behavior. Inflammatory myofibroblastic tumor and infantile fibrosarcoma are neoplasms that have myofibroblastic features and have been included in this category, but they have distinctive genetic findings. This article reviews the concept of myofibrosarcoma and describes its variants.

Myofibrosarcoma

Myofibrosarcomas are malignant tumours of myofibroblasts, which have been recognised for many years, but have become clearly defined only recently. They are low- or high-grade sarcomas that arise in soft tissue or bone in adults or children. Low-grade myofibrosarcomas are infiltrative tumours, usually in deep soft tissue, with a predilection for the head and neck region, which display a range of microscopic appearances from fasciitis-like to fibrosarcoma-like; all cases at least focally display nuclear pleomorphism. They express smooth-muscle actin and calponin, and some express desmin, but most lack h-caldesmon. Low-grade myofibrosarcomas can recur but rarely metastasise. Their differential diagnosis is from benign myofibroblastic proliferations, such as fasciitis and fibromatosis, as well as from fibrosarcoma and leiomyosarcoma. Pleomorphic myofibrosarcomas are high-grade pleomorphic sarcomas (malignant fibrous histiocytoma), which show ultrastructural evidence of myofibroblastic differentiation. They closely resemble malignant fibrous histiocytoma clinically and morphologically, but are more frequently actin positive. This article describes the low- and high-grade variants of myofibrosarcoma and other malignant tumours with myofibroblastic differentiation.

H-caldesmon expression in myofibroblastoma of the breast: evidence supporting the distinction from leiomyoma

AIMS

The ultrastructural detection of leiomyomatous rather than myofibroblastic features in some cases of myofibroblastoma of the breast led some electron microscopically orientated pathologists to doubt the commonly accepted myofibroblastic nature of such a tumour, so the alternative terms 'myogenic stromal tumour' or 'variant of leiomyoma' have been proposed. The aim of this study was to analyse the immunohistochemical expression of h-caldesmon, a reliable marker in distinguishing smooth muscle versus myofibroblastic cellular differentiation, in a large series of myofibroblastomas of the breast to clarify whether these tumours are basically leiomyomatous. Moreover, cases from primary myofibroblastic lesions of the breast, such as fibromatosis and inflammatory myofibroblastic tumour, were analysed to assess whether h-caldesmon expression parallels that observed in their soft tissue counterparts.

METHODS AND RESULTS

Paraffin-embedded sections from 12 cases of myofibroblastoma, seven cases of fibromatosis, and one case of inflammatory myofibroblastic tumour were evaluated immunocytochemically for the expression of h-caldesmon. As expected, all myofibroblastic lesions failed to express h-caldesmon. Conversely, focal staining, ranging from 2% to 10% of neoplastic cells, was detected in myofibroblastomas, even though it was restricted to 50% of analysed cases.

CONCLUSIONS

Our results, indicating that smooth muscle differentiation occurs in a minority of the myofibroblastoma cells exclusively in half of the analysed cases, support the separation of myofibroblastoma from leiomyoma. The detection of smooth muscle cells in breast myofibroblastoma is easily explained if we postulate its histogenesis from the CD34+ fibroblasts of mammary stroma capable of multidirectional mesenchymal differentiation, including smooth muscle. We recommend retention of the term myofibroblastoma for all the desmin-positive and/or alpha-smooth muscle actin-positive spindle cell tumours of the breast consistent with the previously well-established morphological criteria for such neoplasms, unless one is dealing with a typical leiomyoma easily recognizable at light microscopy.