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Mesenchymal chondrosarcomas (MCS) are rare highly malignant chondrosarcomas with a biphasic morphology of a primitive mesenchymal tumor and a well-differentiated cartilaginous component.
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Mesenchymal chondrosarcomas are rare tumors and make up for ~2-4% of all chondrosarcomas 1. They occur in a wide age range and peak in the second and third decades of life 1-3. They are slightly more common in men 1,3.
The diagnosis of mesenchymal chondrosarcomas is established by histology and molecular pathology 1.
Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 1:
undifferentiated tumor cells with a high nuclear-cytoplasm ratio
islands of cartilage
The following criteria are desirable 1:
presence of a staghorn vascular pattern
Mesenchymal chondrosarcomas are highly malignant neoplasms of bone and soft tissues with a biphasic histomorphology of a small round cell sarcoma with islands of hyaline cartilage 1-6. They are thought to arise from chondroblasts 1.
At the time of writing, the etiology of mesenchymal chondrosarcomas is unknown 1.
Mesenchymal chondrosarcomas feature a widespread anatomical distribution and are found in the bone as well as extraskeletal sites including the somatic soft tissues and intracranial sites 1.
The most common skeletal sites involve the following 1,4:
craniofacial bones: ~50%
ribs and chest wall: ~20-25%
spine and sacrum: ~15-20%
lower extremity: ~10-15%
Extraskeletal sites include the somatic soft tissues, the meninges and orbits 1,5. Other sites include the uterus and nasal cavity. Visceral locations are uncommon and include the kidney 1.
Grossly, mesenchymal chondrosarcomas are lobulated firm to soft masses with a variable color ranging from tannish-white to grey or pink 1,4,5 with foci of hemorrhage and necrosis as well as calcified deposits 1.
Histologically, mesenchymal chondrosarcomas are characterized by a biphasic histomorphology with the following features 1-5:
undifferentiated small to medium-sized round or spindled cells with a high nuclear-cytoplasmic ratio
hemangiopericytoma-like staghorn vascular pattern
various islands of well-differentiated hyaline cartilage
possible appearance or mimic of osteoid formation
Immunohistochemistry stains might be positive for S100, CD99, SOX9 and vimentin 1,4. Smooth muscle actin, GFAP and keratins are typically negative 1.
The tumor is also negative for FLI-1, which can be helpful in the differentiation from Ewing sarcoma 1,5. Expression of SMARCB1 (INI-1) is retained which can be helpful for the differentiation from other soft tissue tumors including extraskeletal myxoid chondrosarcoma, epithelioid sarcoma and myoepithelial carcinoma 1,5.
Mesenchymal chondrosarcomas are characterized by HEY1-NCOA2 rearrangements 1,6.
Radiographic features of mesenchymal chondrosarcomas include the following 4,6,7:
eccentric osteolytic lesions
intralesional ring-and-arc or irregular calcifications
permeative or moth-eaten bone destruction
cortical destruction or breakthrough
Imaging features include the following 6:
chondroid calcifications (in the majority of cases ~80%)
biphasic appearance (in about 1/3 of cases): separated calcified and non-calcified zones
hyperintense lobules on T2 weighted images (in about 1/3 of cases)
T1: low to intermediate signal (vs muscle)
T2: hyperintense lobules in about one-third of the lesions 6
T1 C+ (Gd): septal and peripheral enhancement
PET-CT shows increased uptake of FDG 6.
The radiological report should include a description of the following 6-8:
tumor size and location (metaphysis, diaphysis)
presence of metastases
Treatment and prognosis
Mesenchymal chondrosarcomas are aggressive neoplasms with 5-year and 10-year survival rates ranging around ~60% and ~40% 1,9. Management includes complete resection combined with chemotherapy or radiotherapy 1,3-5.
Young adults and children tend to have better outcomes as well as a craniofacial origin, whereas an axial origin and distant metastases at initial presentation are associated with a poorer prognosis 1.
Complications include local recurrences and distant metastases, the latter can occur as late as >20 years after an initial presentation 1.
History and etymology
Mesenchymal chondrosarcomas were first described by the American pathologists Louis Lichtenstein and Donald Bernstein in 1959 4,10.
The differential diagnoses of mesenchymal chondrosarcoma are highly dependent on the location of the tumor, within the bone it includes the following:
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