Bone & joints
Osteosarcoma
Low grade (central) osteosarcoma


Topic Completed: 24 November 2020

Minor changes: 8 January 2021

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PubMed Search: low grade central osteosarcoma[title]

Borislav A. Alexiev, M.D.
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Cite this page: Alexiev BA. Low grade (central) osteosarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/boneLGcentralosteo.html. Accessed April 15th, 2021.
Definition / general
  • Low grade central osteosarcoma (LGCOS) is a low grade malignant bone forming neoplasm that originates within the medullary cavity and consists of fibroblastic tumor cells with low grade nuclear atypia and well formed neoplastic bony trabeculae
Essential features
  • Predominantly fibroblastic osteosarcoma with mild nuclear atypia and well formed neoplastic bony trabeculae
  • Intramedullary location
  • MDM2 amplification
  • Good prognosis when widely resected
Terminology
  • Well differentiated intramedullary osteosarcoma
ICD coding
  • ICD-O: 9187/3 - Low grade central osteosarcoma
  • ICD-11: 2B51.Z & XH7N84 - Osteosarcoma of bone and articular cartilage of unspecified sites & low grade central osteosarcoma
Epidemiology
Sites
Pathophysiology
Etiology
  • Unknown
Clinical features
Diagnosis
  • Tissue sampling is the gold standard for a definitive diagnosis
  • When the radiologic diagnosis suggests a nontypical osseous lesion, clinicians should exercise caution during follow up of the lesion after the initial biopsy results in a benign diagnosis (Int J Clin Oncol 2014;19:731)
  • Open biopsy is better to obtain additional samples (Int J Clin Oncol 2014;19:731)
  • Lack of MDM2 amplification cannot exclude the diagnosis
  • Any difficult or nondiagnostic biopsies of solitary bone lesions should be referred to specialist tumor units for a second opinion (Sarcoma 2012;2012:764796)
Radiology description
Radiology images

Contributed by Borislav A. Alexiev, M.D.

MRI of tibia mass

Prognostic factors
Case reports
Treatment
  • Most important factor in adequate treatment is an accurate diagnosis
  • Should be treated by wide excision, even after intralesional excision, because intralesional excision alone leads to a poorer prognosis (Cancer 1993;71:338, Int J Clin Oncol 2014;19:731)
  • Dedifferentiated LGCOS patients are treated with chemotherapy largely according to regimens for conventional osteosarcoma (Bone Joint J 2019;101-B:745)
Gross description
  • Most often affects the metaphysis of a long bone
  • Usually poorly circumscribed, a feature reflecting infiltrative growth
  • Tumor sometimes has a well defined margin
  • White rubbery fibrous cut surface with gritty calcifications, located in the medullary cavity
  • Cortical destruction and soft tissue infiltration may be present
  • References: Clin Sarcoma Res 2018;8:16, Pathol Int 2003;53:115
Gross images

Contributed by Borislav A. Alexiev, M.D.

Bone mass

Frozen section description
  • Cellular fascicles of spindle cells with mild nuclear atypia admixed with neoplastic bone component
Microscopic (histologic) description
  • Mildly to moderately cellular fascicles of spindle (fibroblast-like) cells with mild nuclear atypia embedded in a fibrosclerotic stroma
  • Neoplastic bone component which typically consists of irregular anastomosing long and thick bony trabeculae, often in parallel arrangement
  • Bone is woven or lamellar
  • Pagetoid bone may be present (Mod Pathol 2004;17:288)
  • Invasive growth pattern (infiltration of the medullary spaces with encasement of preexisting trabeculae)
  • Cortical destruction and soft tissue infiltration may be present
  • Low mitotic activity (Cancer 1977;40:1337)
  • Cartilage formation may be focally present (Cancer 1990;65:1418)
  • Some tumors focally lack bone matrix
  • Can progress high grade sarcoma (dedifferentiation) (Hum Pathol 2000;31:615)
  • High grade areas often show high grade osteosarcoma histology
  • Variant morphology
Microscopic (histologic) images

Contributed by Borislav A. Alexiev, M.D.

Cortical destruction

Well formed neoplastic bone trabeculae

Fascicles of spindle cells

Lack of bone matrix

Mild nuclear atypia

Negative stains
Electron microscopy description
  • Predominant cells are fibroblasts with well developed rough endoplasmic reticulum
  • Few osteoblasts and myofibroblasts
  • Transition cells between fibroblasts and osteoblasts
  • Presence of osteoid matrix
  • Reference: Ultrastruct Pathol 2006;30:293
Molecular / cytogenetics description
Molecular / cytogenetics images

Contributed by Madina Sukhanova, Ph.D.

MDM2 FISH

Sample pathology report
  • Bone, left distal tibia, excision:
    • Low grade osteosarcoma (see comment)
    • Comment: Magnetic resonance imaging shows an enhancing lesion involving the distal tibial metadiaphysis with marked cortical scalloping. The lesion extends to the epiphysis. Hematoxylin eosin stained tissue sections show moderately cellular fascicles of spindle cells with mild nuclear atypia embedded in a fibrosclerotic stroma admixed with a neoplastic bone component, which consists of irregular anastomosing bony trabeculae. Permeation of host bone (infiltration of the medullary spaces with encasement of preexisting trabeculae) is present. Mitoses are extremely rare (1/10 high power fields). FISH shows MDM2 amplification in tumor cells. The findings support the diagnosis of low grade osteosarcoma. Low grade osteosarcoma has a good prognosis, when widely resected, with metastatic rate of < 5%.
Differential diagnosis
Board review style question #1

A 27 year old man presents with a left proximal femur mass. Hematoxylin eosin stained tissue sections show moderately cellular fascicles of spindle cells with mild nuclear atypia embedded in a fibrosclerotic stroma admixed with a neoplastic bone component. Infiltration of the medullary spaces with encasement of preexisting trabeculae and cortical destruction is present. Mitoses are extremely rare (1/10 high power fields). Immunohistochemical stain for MDM2 is positive in tumor cells while all of the following are negative: S100, AE1 / AE3, CD34, ERG and h-caldesmon. FISH studies demonstrate amplification of MDM2 (12q15).

Which of the following is most likely the correct diagnosis?

  1. Low grade osteosarcoma
  2. Ossifying fibromyxoid tumor
  3. Adamantinoma
  4. Fibrous dysplasia
  5. Desmoplastic fibroma
Board review style answer #1
Board review style question #2

Which of the following is true about low grade central osteosarcoma?

  1. Most often affects jaw bones
  2. Has a good prognosis with a metastatic rate of < 5%
  3. Is the most common primary sarcoma of the skeleton
  4. GNAS mutation is common
  5. Presence of cortical disruption and soft tissue infiltration rules out the diagnosis
Board review style answer #2
B. Has a good prognosis with a metastatic rate of < 5%

Comment Here

Reference: Low grade intraosseous (central) osteosarcoma
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