Primary juxtacortical myoepithelioma/mixed tumor of the bone: a report of 3 cases with clinicopathologic, immunohistochemical, ultrastructural, and molecular characterization

Myoepithelioma of bone: ultrastructural, immunohistochemical and molecular study of three cases

Primary intraosseous myoepithelial tumors are rare neoplasms with only a handful of cases described in the medical literature. To date, intraosseous variant of benign myoepithelioma, due to its rarity, has not been studied ultrastructurally, and only one case of a malignant intraosseous myoepithelioma has been described. Three cases were retrieved from the files at the Massachusetts General Hospital (MGH). A diagnosis of benign myoepithelioma was made in case 1 and malignant epithelioma in cases 2 and 3. Ultrastructurally, intermediate filaments (without dense bodies) were found in each case with an abundance in case 1 and lesser amounts in cases 2 and 3. Surprisingly, cell junctions were not identified in case 1. However, they were found occasionally as intermediate junctions in case 2 and were easily identified as desmosome like junctions in case 3. The nucleus was irregular in the neoplastic cells of benign myoepithelioma which contrasted with cases 2 and 3 where the nuclei were oval yet had visible nucleoli. Herein, we add three new cases, including two new cases of malignant myoepithelioma. We also provide the first ultrastructural description of benign myoepithelioma of bone.

Clinicopathologic Features of Two Rare Cases of Dedifferentiated Adamantinomas, Including Diagnostic Implications

A dedifferentiated adamantinoma is a rare subtype of an adamantinoma, associated with a relatively aggressive clinical course, with less than 10 such cases reported so far. A 25-year-old-male presented with pain in his right leg of 1-year duration. Imaging disclosed a well-defined lytic, destructive lesion in his proximal tibia with a cortical break and a soft tissue component. Microscopic examination of the biopsy and resected specimen showed nests and clusters of atypical epithelial cells, along with significant areas showing markedly pleomorphic and spindly sarcomatous cells with interspersed mitotic figures and areas of stromal hyalinization. By immunohistochemistry, the areas of epithelial differentiation showed intense positivity for cytokeratin and p63, whereas the sarcomatous areas showed reduced to absent immunostaining. A 51-year-old lady presented with a recurrent tumor in her right tibia, which was initially diagnosed as an adamantinoma, along with metastatic lesions in her lung. Microscopic examination of the recurrent and metastatic tumors showed areas of epithelial differentiation along with spindly sarcomatous cells, arranged in fascicles. By immunohistochemistry, the areas of epithelial differentiation showed positivity for pan cytokeratin. Additionally, p63 was diffusely positive. p53 showed diffuse and intense staining pattern in the sarcomatous component (dedifferentiation). While the first case is disease-free, the second case is on follow-up. The 2 cases of dedifferentiated adamantinoma further confirm the rare occurrence of this tumor in our population. Its correct diagnosis has treatment implications. Differential diagnoses and literature review of similar reported cases are also presented in this article.

Myoepithelial Tumors of Bone

Myoepithelial tumors (METs) of bone (BMETs) are a rare but distinct tumor entity. METs that are cytologically benign are termed myoepitheliomas; METs with malignant histologic features are called myoepithelial carcinomas. BMETs have a wide age range, may involve any part of the skeleton, and have a variable spindle cell and epithelioid morphology. Bone tumors to be considered in the differential diagnosis are discussed. Additional techniques are indispensable to correctly diagnose BMETs. By immunohistochemistry, BMETs often express cytokeratins and/or EMA together with S100, GFAP, or calponin. Half of BMETs harbor EWSR1 (or rare FUS) gene rearrangements with different gene partners.

Primary intra-osseous myoepithelioma of phalanx mimicking an enchondroma

Myoepitheliomas (MEs) are uncommon tumours of the soft tissue with an intermediate biological behaviour and uncertain differentiation. Primary intra-osseous MEs are rare and occur predominantly in the axial and proximal appendicular skeleton in middle-aged patients. The morphological variation of the tumour cells and stromal metaplasia may cause considerable diagnostic confusion, especially when it occurs in an unusual location. A wide panel of immunohistochemical markers is required to exclude other histological mimics. A 37-year-old male presented with a recurrent swelling in the right middle finger for 1-month duration. Radiographic images showed an expansile, lytic, intra-osseous lesion with high signal intensity on T2W fat-suppressed MR images in the proximal phalanx of the right middle finger without cortical breach, highly suggestive of an enchondroma. Histopathology revealed a lobulated tumour comprising of polygonal to spindle cells in groups and cords in a chondromyxoid stroma. No cellular atypia was noted. The tumour cells were immunopositive for epithelial membrane antigen (EMA), p63, S100 and smooth muscle actin (SMA), compatible with the diagnosis of an intraosseous ME. The proximal phalanx of the right middle finger was excised, revealing a similar tumour, and the patient has been on regular follow-up for the last 18 months without any recurrence. Primary intra-osseous MEs are extremely rare, and this is the second reported occurrence in small bones. A differential diagnosis of ME should be kept for enchondroma-like lesions of the bone for proper histopathological assessment and accurate diagnosis. Documentation of such cases and follow-up will enhance our understanding of their clinical course and prognosis.

Myxoid liposarcoma with pleomorphic cells: Report of two cases with molecular confirmation of FUS gene rearrangements

Myxoid liposarcoma is usually composed of uniform oval to short spindle cells in a prominent myxoid stroma. We report here two cases of myxoid liposarcoma containing unusual pleomorphic cells harboring FUS gene rearrangements. One of the lesions arose in the right loin of a 70-year-old man, while the other in the right upper arm of a 73-year-old woman. Both tumors were composed of a lobular proliferation of short spindle to oval cells, admixed with lipoblastic cells and scattered pleomorphic cells including pseudolipoblast-like or Touton-type giant cell-like cells, embedded in an abundant myxoid stroma containing a network of delicate capillary vessels. An FUS gene rearrangement was detected by fluorescence in situ hybridization in one case, and an FUS-DDIT3 fusion gene transcript by reverse transcription-polymerase chain reaction in the other. These unique cases focus our attention to a much wider histological variation of myxoid liposarcoma than expected, as well as to the value of molecular testing for final diagnosis of such myxoid sarcomas.

Clinicopathological features of five unusual cases of intraosseous myoepithelial carcinomas, mimicking conventional primary bone tumours, including EWSR1 rearrangement in one case

Primary intraosseous myoepithelial tumours, including carcinomas are rare tumours. The concept of histopathological spectrum of these tumours is evolving. We describe clinicopathological and immunohistochemical features of five myoepithelial carcinomas, including molecular cytogenetic results in one case. There were five male patients within age-range of 8-40 years (median = 26). Four tumours occurred in the long bones, including two tumours, each, in the femur and fibula, respectively, while a single tumour occurred in the proximal phalanges. Tumour size (n = 3 cases) varied from 5.6 to 8.6 cm. On radiological imaging, most tumours appeared as expansile, lytic and destructive lesions. Two tumours appeared as sclerotic lesions. Two cases were referred with diagnoses of chondrosarcomas and a single case was referred with two different diagnoses, including an adamantinoma and an osteosarcoma. Histopathological examination in all these cases showed multinodular tumours comprising mostly polygonal cells, exhibiting moderate nuclear atypia and interspersed mitotic figures within a stroma containing variable amount of myxoid, chondroid, hyalinised and osteoid-like material. Three tumours revealed prominent squamous differentiation. By immunohistochemistry, tumour cells were positive for EMA (5/5), pan CK (AE1/AE3) (3/3), CK5/6 (4/4), CK MNF116 (1/1), S100 protein (5/5) and GFAP (3/5). The first tumour revealed EWSR1 rearrangement. The first patient, 10 months after tumour resection and a simultaneous lung metastatectomy, is free-of-disease (FOD). The second patient, 11 months after tumour resection is FOD. The third and fourth patients underwent wide resections and are on follow-up. The fifth patient underwent resections, including a lung metastatectomy. Primary intraosseous myoepithelial carcinomas are rare and mimic conventional primary bone tumours. Some primary intraosseous myoepithelial carcinomas display EWSR1 rearrangement. Squamous differentiation may be considered as an addition to their evolving histopathological spectrum. Immunohistochemical stains constitute as a necessary tool for arriving at the correct diagnosis in such cases, which has treatment implications. Surgical resection remains the treatment mainstay.

Myoepithelial Tumors: An Update

Primary myoepithelial neoplasms of soft tissue are uncommon, and have been increasingly characterized by clinicopathologic and genetic means. Tumors are classified as mixed tumor/chondroid syringoma, myoepithelioma, and myoepithelial carcinoma, and they share morphologic, immunophenotypic, and genetic features with their salivary gland counterparts. However, soft tissue myoepithelial tumors are classified as malignant based on the presence of cytologic atypia, in contrast to the criterion of invasive growth in salivary gland sites. This review discusses the clinicopathologic and morphologic characteristics, distinct variants, and currently known genetic alterations of myoepithelial neoplasms of soft tissue, skin, and bone.

A histological surprise: a rare case of myoepithelial tumour of the scrotum and review of literature

A lump in the scrotum is a common presentation in most surgical clinics. However, myoepithelial tumours may not be up on the list of differentials. Although they may look benign, myoepithelial tumours are rare and have malignant potential. Treatment of these tumours involved total excision and adequate follow-up in cases of malignancy. These groups of tumours have not been reported in the scrotum in the past, but their occurrence in the vagina may not come as a surprise bearing in mind the embryonic origin of both organs.