Low-grade fibromyxoid sarcoma | |
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Micrograph of a low-grade fibromyxoid sarcoma. H&E stain. | |
Specialty | Pathology |
Low-grade fibromyxoid sarcoma (LGFMS) is a rare type of low-grade sarcoma first described by H. L. Evans in 1987. [1] LGFMS are soft tissue tumors of the mesenchyme-derived connective tissues; on microscopic examination, they are found to be composed of spindle-shaped cells that resemble fibroblasts. [2] These fibroblastic, spindle-shaped cells are neoplastic cells that in most cases of LGFMS express fusion genes, i.e. genes composed of parts of two different genes that form as a result of mutations. [2] The World Health Organization (2020) classified LGFMS as a specific type of tumor in the category of malignant fibroblastic and myofibroblastic tumors. [3]
LGFMS tumors occur in individuals of almost any age but up to 20% are less than 18 years/old. The tumors typically involve the proximal extremities but can occur virtually anywhere in the body. [4] The progression of these tumors commonly takes an indolent, prolonged course involving many years or decades. Over this time, however, the tumors often recur at the site of their surgical removal and/or metastasize usually to the lung or pleural tissues surrounding the lungs. [5] These metastasis can develop decades after the tumor's initial presentation and diagnosis. [6]
LGFMS can be difficult to distinguish from other mesenchymal tumors, [7] particularly from sclerosing epithelioid fibrosarcoma (SEF). [8] LGFMS tumors present with many clinical and pathological features that are similar to those in SEF. Indeed, current studies suggest that LGFMS may be an early form of SEF. For example, a tumor may present with features typical of LGFMS but over time progress to features typical of sclerosing epithelioid fibrosarcomas. This progression may be particularly evident in recurrent or metastatic "LGFMS" tumors. [8] [9] Since the World Health Organization has classified LGFMS as one of the malignant fibroblastic and myofibroblastic tumors that is distinctly different than SEF, [3] SEF and LGFMS are here regarded as separate tumor forms.
Individuals initially diagnosed with LGFMS had been characterized as young adults (mean age: 33 years) or children >5 years old (13% to 19% of all cases), [10] although a more recent study reported that individuals first diagnosed with the disease ranged in age between 6 and 67 years (mean age: 45.6 year). [8] LGFMS generally presents as a painless mass located in the subcutaneous or subfacial (i.e. beneath the skin) tissues of the upper or lower limbs, trunk, [4] or, less commonly, the head and neck areas or within the gastrointestinal tract, heart, kidney, brain, [11] retroperitoneum, mediastinum, or abdominal cavity. [4] Tumors occurring in subcutaneous and subfacial tissues are often 3–11 cm in size (largest diameter) [8] but in sites where the tumor can go undetected for long periods such as the buttocks, [8] mediastinum, [12] or abdominal cavity [13] have been reported to be as large as 25, 23.5, and 50 cm, respectively. Magnetic resonance imaging and computed tomography scans often give results suggesting that a tumor is a LGFMS. [4] [14]
LGMFS tumors typically contain one or multiple nodules embedded in a grey-white whorled cut surface. They appear to be infiltrating adjacent structures/tissues in a minority of cases. Microscopic histopathologic views of hematoxylin and eosin stained tumor tissue show whorled and bundled, uniform, bland-appearing, slender fibroblastic spindle-shaped cells with elongated, tapered nuclei. The cells have scant cytoplasm and do not appear to be rapidly proliferating as defined by their low rate of mitosis. The spindle-shaped cells typically occur in an alternating fibrous and myxoid (i.e. more blue or purple compared to normal connective tissue because of excessive uptake of the hematoxylin stain) background. However, the tissues may contain sites dominated by epithelioid cells and other elements that resemble, [2] or are indistinguishable from, [5] sclerosing epithelioid fibrosarcoma. This hybrid pattern is more often seen in recurrent and metastatic LGGMS tumors, may progress to dominate the tissues, and may therefore warrant changing the diagnosis of LGFMD to sclerosing epithelioid fibrosarcoma. [2] While not definitive, LGMFS tumors that are dominated with cells that have an undifferentiated or immature round-cell morphology may be more aggressive than tumors with the typical cell morphology. [2]
Immunohistochemical analyses of LGFMS tumors shows cells that express: MUC1 (also termed EMA), CD99, and/or bcl-2 proteins in some cases; CD34 and SMA proteins in rare cases; and S100, desmin, caldesmon, cytokeratin, and CD117 proteins in virtually no cases. [10] However, MUC4 protein is express by the tumor cells of almost all LGFMS cases [10] and therefore is commonly used as a sensitive and specific marker for LGFMS. [4] [5] [10] (Since a small subset of LGFMS tumors have been reported to consist of cells that are MUC4-negative, the diagnosis of LGFMS should not be absolutely dependent on finding MUC4-positive tumor cells. [8] )
The neoplastic cells in LGFMS tumors express one of various fusion genes. Fusion genes are abnormal genes consisting of parts of two different genes that merge as a result of large scale gene mutations such as chromosomal translocations, interstitial deletions, or inversions. The fusion genes in LGFMS merge part of the FUS or EWSR2 gene (which is one of the FET protein family genes) with part of a CREB3L2 (i.e. cAMP responsive element binding protein 3 like 2 gene [15] ) or CREB3L1 (i.e. CAMP responsive element binding protein 3 like 1 gene). A FUS-CREB3L2 fusion gene is expressed in the majority of LGMFS cases while a FUS-CREB3L1, [16] EWSR1-CREB3L2, or EWSR2-CREBL1 [2] fusion gene is expressed in a minority of LGMFS cases. Fusion genes containing part of an AFET gene family gene occur in a wide range of tumors and are though to contribute to the development of at least some of these tumors. [17] [18] While the role of the cited fusion genes in the development of LGFMS is not known, the presence of one of these fusion genes is helpful in diagnosing the disease. [10] [13]
The diagnosis of LGFMS rest primary on its tumors' histology consisting of spindle-shaped fibroblastic cells in the appropriate background that express the MUC4 protein and either a FUS-CREB3L2, FUS-CREB3L1, EWSR1-CREB3L2, or EWSR2-CREBL1 fusion gene in most cases. [8] Magnetic resonance imaging and computed tomography scan findings ma also help in the diagnosis. [4] These findings can differentiate LGFMS from various spindle-shaped cell and myxoid neoplasms including benign soft tissue tumors, malignant soft tissue tumors (e.g. desmoid fibromatosis), and sarcomas (e.g., malignant peripheral nerve sheath tumora, low-grade myxofibrosarcoma, myxoid dermatofibrosarcoma protuberans, or in rare cases, extraskeletal myxoid chondrosarcoma, synovial sarcomas that have a prominent myxoid background, or myxoid liposarcoma. [8] However, sclerosing epithelioid fibrosarcoma tumors may contain areas that are histopathologically indistinguishable from LGFMS [2] and contain neoplastic cells that expression MUC4 protein in most cases, [19] and a EWSR1-CREB3L1 fusion gene in >20% of cases, a FUS-CREB3L2 fusion gene in ~10% of cases, or a EWSR1-CREB3L2 fusion gene in rare cases. [20] Based on the relative rates of expression in the two tumor types, the presence of tumor neoplastic cells that: 1) express the MUC4 marker protein and a FUS-CREB3L2 fusion gene or an otherwise rearranged FUS gene strongly suggest that the tumor is a SEF; [21] 2) express the EWSR1-CREB3L1 fusion gene suggest that the tumor is a SEF [20] but in any case is unlikely to be a low-grade fibromyxoid sarcoma. [21] 3) express a FUS-CREB3L2 fusion gene is more likely to be a low-grade fibromyxoid sarcoma than a SEF (i.e. the FUS-CREB3L2 fusion gene is present in >90% of low-grade fibromyxoid sarcomas but only ~20% of SEF tumor cells}; [22] or 4) express an EWSR1-CREB3L1 or EWSR1-CREB3L2 fusion gene is likely to be a SEF tumor. [19]
The generally recommended treatment for LGFMS is aggressive, wide surgical excision of the tumor [8] including even those located in difficult to access sites such as the mediastinum. [12] Complete removal of all tumor tissue is critical in lowering the rates of recurrences and metastases. [6] Over the long term, surgically resected LGFMS tumors have tended to recur at the site or resection in up to 75% of cases. [11] These recurrences can develop as long as 15 years (median: 3.5 years) after the initial diagnosis of the disease. [6] Following initial surgical resection, metastases have been reported to develop in up to 50% of individuals. [11] These metastases have been diagnosed up to 45 years (median: 5 years) after the initial diagnosis of LGFMS. They were found mostly in the lungs, pleura, and chest wall, occasionally in the pericardium (i.e. the sac containing the heart), and rarely in a bone, the liver, or the heart. [6] Recurrences of the tumors at the site of their resection as well as many of their metastases have been treated by surgical resections; this treatment may be repeated multiple times in individuals who develop repeated local recurrences and/or metastases. Radiation therapy combined with partial surgical resection or radiation therapy alone have been used in cases where the primary, recurrent, or metastatic tumor cannot be safely or totally removed. [7] [10] [6] However, the experiences with radiation therapy and chemotherapy to treat LGFMS are limited and this tumor does not appear very sensitive to either treatment modality. [5] In one long-term study of 33 treated individuals with LGFMS, 14 died of their tumors from 3 to 42 years (median: 15 years) after their initial diagnosis and 19 were alive after 5½ to 70 years (median: 13 years] of their diagnosis with 6 individuals having persistent tumors and 13 being tumor-free. [6]
A sarcoma is a malignant tumor, a type of cancer that arises from cells of mesenchymal origin. Connective tissue is a broad term that includes bone, cartilage, fat, vascular, or other structural tissues, and sarcomas can arise in any of these types of tissues. As a result, there are many subtypes of sarcoma, which are classified based on the specific tissue and type of cell from which the tumor originates. Sarcomas are primary connective tissue tumors, meaning that they arise in connective tissues. This is in contrast to secondary connective tissue tumors, which occur when a cancer from elsewhere in the body spreads to the connective tissue. Sarcomas are one of five different types of cancer, classified by the cell type from which they originate. The word sarcoma is derived from the Greek σάρκωμα sarkōma 'fleshy excrescence or substance', itself from σάρξsarx meaning 'flesh'.
Dermatofibrosarcoma protuberans (DFSP) is a rare locally aggressive malignant cutaneous soft-tissue sarcoma. DFSP develops in the connective tissue cells in the middle layer of the skin (dermis). Estimates of the overall occurrence of DFSP in the United States are 0.8 to 4.5 cases per million persons per year. In the United States, DFSP accounts for between 1 and 6 percent of all soft-tissue sarcomas and 18 percent of all cutaneous soft-tissue sarcomas. In the Surveillance, Epidemiology and End Results (SEER) tumor registry from 1992 through 2004, DFSP was second only to Kaposi sarcoma.
Liposarcomas are the most common subtype of soft tissue sarcomas, accounting for at least 20% of all sarcomas in adults. Soft tissue sarcomas are rare neoplasms with over 150 different histological subtypes or forms. Liposarcomas arise from the precursor lipoblasts of the adipocytes in adipose tissues. Adipose tissues are distributed throughout the body, including such sites as the deep and more superficial layers of subcutaneous tissues as well as in less surgically accessible sites like the retroperitoneum and visceral fat inside the abdominal cavity.
Fibrosarcoma is a malignant mesenchymal tumour derived from fibrous connective tissue and characterized by the presence of immature proliferating fibroblasts or undifferentiated anaplastic spindle cells in a storiform pattern. Fibrosarcomas mainly arise in people between the ages of 25 and 79. It originates in fibrous tissues of the bone and invades long or flat bones such as the femur, tibia, and mandible. It also involves the periosteum and overlying muscle.
Congenital mesoblastic nephroma, while rare, is the most common kidney neoplasm diagnosed in the first three months of life and accounts for 3-5% of all childhood renal neoplasms. This neoplasm is generally non-aggressive and amenable to surgical removal. However, a readily identifiable subset of these kidney tumors has a more malignant potential and is capable of causing life-threatening metastases. Congenital mesoblastic nephroma was first named as such in 1967 but was recognized decades before this as fetal renal hamartoma or leiomyomatous renal hamartoma.
A myxoid liposarcoma is a malignant adipose tissue neoplasm of myxoid appearance histologically.
Clear cell sarcoma is a rare form of cancer called a sarcoma. It is known to occur mainly in the soft tissues and dermis. Rare forms were thought to occur in the gastrointestinal tract before they were discovered to be different and redesignated as gastrointestinal neuroectodermal tumors.
Extraskeletal myxoid chondrosarcoma (EMC) is a rare low-grade malignant mesenchymal neoplasm of the soft tissues, that differs from other sarcomas by unique histology and characteristic chromosomal translocations. There is an uncertain differentiation and neuroendocrine differentiation is even possible.
Inflammatory myofibroblastic tumor (IMT) is a rare neoplasm of the mesodermal cells that form the connective tissues which support virtually all of the organs and tissues of the body. IMT was formerly termed inflammatory pseudotumor. Currently, however, inflammatory pseudotumor designates a large and heterogeneous group of soft tissue tumors that includes inflammatory myofibroblastic tumor, plasma cell granuloma, xanthomatous pseudotumor, solitary mast cell granuloma, inflammatory fibrosarcoma, pseudosarcomatous myofibroblastic proliferation, myofibroblastoma, inflammatory myofibrohistiocytic proliferation, and other tumors that develop from connective tissue cells. Inflammatory pseudotumour is a generic term applied to various neoplastic and non-neoplastic tissue lesions which share a common microscopic appearance consisting of spindle cells and a prominent presence of the white blood cells that populate chronic or, less commonly, acute inflamed tissues.
Mammary-type myofibroblastoma (MFB), also named mammary and extramammary myofibroblastoma, was first termed myofibrolastoma of the breast, or, more simply, either mammary myofibroblastoma (MMFB) or just myofibroblastoma. The change in this terminology occurred because the initial 1987 study and many subsequent studies found this tumor only in breast tissue. However, a 2001 study followed by numerous reports found tumors with the microscopic histopathology and other key features of mammary MFB in a wide range of organs and tissues. Further complicating the issue, early studies on MFB classified it as one of various types of spindle cell tumors that, except for MFB, were ill-defined. These other tumors, which have often been named interchangeably in different reports, are: myelofibroblastoma, benign spindle cell tumor, fibroma, spindle cell lipoma, myogenic stromal tumor, and solitary stromal tumor. Finally, studies suggest that spindle cell lipoma and cellular angiofibroma are variants of MFB. Here, the latter two tumors are tentatively classified as MFB variants but otherwise MFB is described as it is more strictly defined in most recent publications. The World Health Organization in 2020 classified mammary type myofibroblastoma tumors and myofibroblastoma tumors as separate tumor forms within the category of fibroblastic and myofibroblastic tumors.
CAMP responsive element binding protein 3 like 1 is a responsive element binding protein that in humans is encoded by the CREB3L1 gene.
Acral myxoinflammatory fibroblastic sarcoma (AMSF), also termed myxoinflammatory fibroblastic sarcoma (MSF), is a rare, low-grade, soft tissue tumor that the World Health Organization (2020) classified as in the category of rarely metastasizing fibroblastic and myofibroblastic tumors. It is a locally aggressive neoplasm that often recurs at the site of its surgical removal. However, it usually grows slowly and in only 1–2% of cases spreads to distant tissues.
Proliferative fasciitis and proliferative myositis (PF/PM) are rare benign soft tissue lesions that increase in size over several weeks and often regress over the ensuing 1–3 months. The lesions in PF/PM are typically obvious tumors or swellings. Historically, many studies had grouped the two descriptive forms of PF/PM as similar disorders with the exception that proliferative fasciitis occurs in subcutaneous tissues while proliferative myositis occurs in muscle tissues. In 2020, the World Health Organization agreed with this view and defined these lesions as virtually identical disorders termed proliferative fasciitis/proliferative myositis or proliferative fasciitis and proliferative myositis. The Organization also classified them as one of the various forms of the fibroblastic and myofibroblastic tumors.
Fibroblastic and myofibroblastic tumors (FMTs) develop from the mesenchymal stem cells which differentiate into fibroblasts and/or the myocytes/myoblasts that differentiate into muscle cells. FMTs are a heterogeneous group of soft tissue neoplasms. The World Health Organization (2020) defined tumors as being FMTs based on their morphology and, more importantly, newly discovered abnormalities in the expression levels of key gene products made by these tumors' neoplastic cells. Histopathologically, FMTs consist of neoplastic connective tissue cells which have differented into cells that have microscopic appearances resembling fibroblasts and/or myofibroblasts. The fibroblastic cells are characterized as spindle-shaped cells with inconspicuous nucleoli that express vimentin, an intracellular protein typically found in mesenchymal cells, and CD34, a cell surface membrane glycoprotein. Myofibroblastic cells are plumper with more abundant cytoplasm and more prominent nucleoli; they express smooth muscle marker proteins such as smooth muscle actins, desmin, and caldesmon. The World Health Organization further classified FMTs into four tumor forms based on their varying levels of aggressiveness: benign, intermediate, intermediate, and malignant.
Lipofibromatosis-like neural tumor (LPF-NT) is an extremely rare soft tissue tumor first described by Agaram et al in 2016. As of mid-2021, at least 39 cases of LPF-NT have been reported in the literature. LPF-NT tumors have several features that resemble lipofibromatosis (LPF) tumors, malignant peripheral nerve sheath tumors, spindle cell sarcomas, low-grade neural tumors, peripheral nerve sheath tumors, and other less clearly defined tumors; Prior to the Agaram at al report, LPF-NTs were likely diagnosed as variants or atypical forms of these tumors. The analyses of Agaram at al and subsequent studies uncovered critical differences between LPF-NT and the other tumor forms which suggest that it is a distinct tumor entity differing not only from lipofibromatosis but also the other tumor forms.
Myxofibrosarcoma (MFS), although a rare type of tumor, is one of the most common soft tissue sarcomas, i.e. cancerous tumors, that develop in the soft tissues of elderly individuals. Initially considered to be a type of histiocytoma termed fibrous histiocytoma or myxoid variant of malignant fibrous histiocytoma, Angervall et al. termed this tumor myxofibrosarcoma in 1977. In 2020, the World Health Organization reclassified MFS as a separate and distinct tumor in the category of malignant fibroblastic and myofibroblastic tumors.
Sclerosing epithelioid fibrosarcoma (SEF) is a very rare malignant tumor of soft tissues that on microscopic examination consists of small round or ovoid neoplastic epithelioid fibroblast-like cells, i.e. cells that have features resembling both epithelioid cells and fibroblasts. In 2020, the World Health Organization classified SEF as a distinct tumor type in the category of malignant fibroblastic and myofibroblastic tumors. However, current studies have reported that low-grade fibromyxoid sarcoma (LGFMS) has many clinically and pathologically important features characteristic of SEF; these studies suggest that LGSFMS may be an early form of, and over time progress to become, a SEF. Since the World Health Organization has classified LGFMS as one of the malignant fibroblastic and myofibroblastic tumors that is distinctly different than SEF, SEF and LGFMS are here regarded as different tumor forms.
The FET protein family consists of three similarly structured and functioning proteins. They and the genes in the FET gene family which encode them are: 1) the EWSR1 protein encoded by the EWSR1 gene located at band 12.2 of the long arm of chromosome 22; 2) the FUS protein encoded by the FUS gene located at band 16 on the short arm of chromosome 16; and 3) the TAF15 protein encoded by the TAF15 gene located at band 12 on the long arm of chromosome 7 The FET in this protein family's name derives from the first letters of FUS, EWSR1, and TAF15.
Angiofibroma of soft tissue (AFST), also termed angiofibroma, not otherwise specified, is a recently recognized and rare disorder that was classified in the category of benign fibroblastic and myofibroblastic tumors by the World Health Organization in 2020. An AFST tumor is a neoplasm that was first described by A. Mariño-Enríquez and C.D. Fletcher in 2012.
Low-grade myofibroblastic sarcoma (LGMS) is a subtype of the malignant sarcomas. As it is currently recognized, LGMS was first described as a rare, atypical myofibroblastic tumor by Mentzel et al. in 1998. Myofibroblastic sarcomas had been divided into low-grade myofibroblastic sarcomas, intermediate‐grade myofibroblasic sarcomas, i.e. IGMS, and high‐grade myofibroblasic sarcomas, i.e. HGMS based on their microscopic morphological, immunophenotypic, and malignancy features. LGMS and IGMS are now classified together by the World Health Organization (WHO), 2020, in the category of intermediate fibroblastic and myofibroblastic tumors. WHO, 2020, classifies HGMS as a soft tissue tumor in the category of tumors of uncertain differentiation. This article follows the WHO classification: here, LGMS includes IGMS but not HGMS which is a more aggressive and metastasizing tumor than LGMS and consists of cells of uncertain origin.