Skip to content
How It Works
Explore
Resources Ask a Question
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Ask a Question
PubMed This is a summary of 23 peer-reviewed journal articles Updated
Oncology

Biology and Diagnosis: Why the "How" and "Who" Matter

At a Glance

Osteosarcoma is an aggressive bone cancer diagnosed by the presence of malignant osteoid. Accurate staging requires a whole-bone MRI and chest CT. The initial biopsy must be done by the specialized surgeon performing the final surgery to prevent tumor spread and protect limb-saving options.

To understand osteosarcoma, it helps to look at it as a critical breakdown in the body’s normal bone-building process. While bone growth is a natural part of childhood and adolescence, osteosarcoma occurs when the biological “brakes” that control this growth fail, leading to an aggressive and uncontrolled production of bone [1][2].

The Genetic “Brakes”: TP53 and RB1

Every cell in the body has instructions for when to grow and when to stop. In osteosarcoma, two specific genes that act as the cell’s primary safety systems are often broken:

  • TP53 (The “Guardian”): Think of TP53 as a quality-control inspector. Its job is to check a cell’s DNA for damage. If it finds a mistake, it stops the cell from dividing until it is fixed—or it tells the cell to self-destruct if the damage is too severe [2][3]. When TP53 is mutated, the inspector is gone, and damaged cells can multiply into a tumor [1].
  • RB1 (The “Gatekeeper”): RB1 controls the “gate” that allows a cell to move from one stage of growth to the next. It prevents cells from dividing too fast [4][1]. In many osteosarcomas, the RB1 gene is lost or inactive, leaving the gate wide open for rapid, unchecked cell division [5][6].

The Diagnostic “Smoking Gun”: Malignant Osteoid

The hallmark of osteosarcoma—what distinguishes it from every other type of bone condition—is the production of malignant osteoid [7][8].

Osteoid is the soft, unmineralized part of new bone. In a healthy child, this eventually hardens into strong bone. In osteosarcoma, the cancer cells directly produce this osteoid themselves, but in a chaotic, malignant way [7][9].

  • Ewing Sarcoma, another common pediatric bone cancer, does not produce osteoid. It is made of “small round blue cells” and requires different genetic testing to identify [10][11].
  • Aneurysmal Bone Cysts (ABC) are benign (non-cancerous) but can look very similar on X-rays. Unlike osteosarcoma, they do not produce malignant osteoid and do not have the same aggressive genetic mutations [12][13].

Precision Diagnosis: Imaging and Biopsy

Because osteosarcoma is aggressive, the diagnostic process must be precise and follow a specific sequence to ensure the best surgical outcome:

Advanced Imaging

  • High-Resolution MRI: This is used to map the tumor’s size and its relationship to nearby nerves and blood vessels. Crucially, a whole-bone MRI is needed to check for skip metastases—small “islands” of tumor that can sit further down the same bone, away from the main mass [14].
  • Chest CT: Because osteosarcoma has a high tendency to spread to the lungs, a detailed CT scan of the chest is a standard part of the initial staging process [15][16].

The “Surgical” Biopsy

The biopsy is the most critical step in the diagnostic journey. A small sample of the tumor is removed (usually via a core needle biopsy) to be examined under a microscope [17][18].

Crucial Warning: The initial biopsy should only be performed by the specialized orthopedic oncologist who will perform the final surgery [19]. This is because the “track” the needle takes to reach the tumor can become contaminated with cancer cells (a process called tumor seeding) [20]. To prevent the cancer from coming back, the surgeon must be able to remove that entire needle track during the definitive surgery [21][22]. If the biopsy is done poorly or in the wrong location by an inexperienced surgeon, it can jeopardize the ability to save the limb [19][23].

Common questions in this guide

What is malignant osteoid in an osteosarcoma diagnosis?
Malignant osteoid is the abnormal, soft bone material produced by osteosarcoma cancer cells. It is the key characteristic that pathologists look for under a microscope to definitively distinguish osteosarcoma from other types of bone tumors or cysts.
Why is it important who performs my child's osteosarcoma biopsy?
The biopsy must be performed by the specialized orthopedic oncologist who will do the final surgery. This ensures the needle track can be completely removed later, preventing cancer cells from spreading and protecting the child's chance for limb-saving surgery.
What are skip metastases in bone cancer?
Skip metastases are small islands of tumor cells that have spread further down the same bone, separated from the main tumor mass. A whole-bone MRI is required to find these spots and plan the proper surgical treatment.
Why do doctors check the TP53 and RB1 genes for osteosarcoma?
TP53 and RB1 act as safety brakes that control normal cell growth. In many osteosarcoma cases, these genes are mutated or inactive, allowing bone cells to multiply rapidly and form an aggressive tumor.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Did the pathology report confirm the presence of 'malignant osteoid' to finalize the diagnosis?
  2. 2.Has our child’s tumor been tested for specific mutations in the TP53 or RB1 genes?
  3. 3.Did the whole-bone MRI show any 'skip metastases' away from the main tumor site?
  4. 4.Will the biopsy tract be completely removed (excised) during the definitive surgery?
  5. 5.How does the pathology team distinguish this tumor from Ewing sarcoma or a telangiectatic bone cyst?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (23)
  1. 1

    The past, present and future of potential small-molecule drugs targeting p53-MDM2/MDMX for cancer therapy.

    Liu Y, Wang X, Wang G, et al.

    European journal of medicinal chemistry 2019; (176()):92-104 doi:10.1016/j.ejmech.2019.05.018.

    PMID: 31100649
  2. 2

    Recent Advances in p53.

    D'Orazi G

    Biomolecules 2021; (11(2)) doi:10.3390/biom11020211.

    PMID: 33546313
  3. 3

    The Rich World of p53 DNA Binding Targets: The Role of DNA Structure.

    Brázda V, Fojta M

    International journal of molecular sciences 2019; (20(22)) doi:10.3390/ijms20225605.

    PMID: 31717504
  4. 4

    An anti-cancer surveillance by the interplay between interferon-beta and retinoblastoma protein RB1.

    Qin A

    Frontiers in oncology 2023; (13()):1173467 doi:10.3389/fonc.2023.1173467.

    PMID: 37182173
  5. 5

    RB1 Deletion in Retinoblastoma Protein Pathway-Disrupted Cells Results in DNA Damage and Cancer Progression.

    Marshall AE, Roes MV, Passos DT, et al.

    Molecular and cellular biology 2019; (39(16)) doi:10.1128/MCB.00105-19.

    PMID: 31138663
  6. 6

    Cell Cycle and Beyond: Exploiting New RB1 Controlled Mechanisms for Cancer Therapy.

    Knudsen ES, Pruitt SC, Hershberger PA, et al.

    Trends in cancer 2019; (5(5)):308-324 doi:10.1016/j.trecan.2019.03.005.

    PMID: 31174843
  7. 7

    Role of extracellular vesicles in osteosarcoma.

    Yang Q, Liu J, Wu B, et al.

    International journal of medical sciences 2022; (19(8)):1216-1226 doi:10.7150/ijms.74137.

    PMID: 35928720
  8. 8

    A Humeral Osteosarcoma Mimicking Osseous Leiomyosarcoma: A Case Report.

    Yan Y, Xie V, Perrin D, et al.

    Cureus 2024; (16(1)):e52469 doi:10.7759/cureus.52469.

    PMID: 38371158
  9. 9

    Fibroblastic osteosarcoma: A perplexing entity.

    Kaur KP, Kundu S, Chatterjee A, Pal M

    Journal of oral and maxillofacial pathology : JOMFP 2023; (27(3)):573-578 doi:10.4103/jomfp.jomfp_496_22.

    PMID: 38033966
  10. 10

    SATB2 immunohistochemistry in osteosarcoma: Utility in diagnosis and differentiation from histologic mimics.

    Gangula S, Hui M, Uppin SG, et al.

    Indian journal of pathology & microbiology 2025; (68(3)):518-525 doi:10.4103/ijpm.ijpm_631_24.

    PMID: 40485468
  11. 11

    The utility of SATB2 immunohistochemical expression in distinguishing between osteosarcomas and their malignant bone tumor mimickers, such as Ewing sarcomas and chondrosarcomas.

    Machado I, Navarro S, Picci P, Llombart-Bosch A

    Pathology, research and practice 2016; (212(9)):811-6.

    PMID: 27465835
  12. 12

    Telangiectatic osteosarcoma of the rib: a rare entity and a potential diagnostic pitfall.

    Saguem I, Ayadi L, Kallel R, et al.

    Pathologica 2016; (108(4)):175-178.

    PMID: 28195259
  13. 13

    Telangiectatic osteosarcoma of maxilla in a young child.

    Jot K, Nayyar V, Manchanda S, et al.

    Oral oncology 2023; (147()):106605 doi:10.1016/j.oraloncology.2023.106605.

    PMID: 37890305
  14. 14

    The sensitivity, specificity, and diagnostic accuracy of whole-bone MRI for identifying skip metastases in appendicular osteosarcoma and Ewing sarcoma.

    Barnett JR, Gikas P, Gerrand C, et al.

    Skeletal radiology 2020; (49(6)):913-919 doi:10.1007/s00256-019-03364-0.

    PMID: 31900513
  15. 15

    Advances in the management of osteosarcoma.

    Bielack SS, Hecker-Nolting S, Blattmann C, Kager L

    F1000Research 2016; (5()):2767 doi:10.12688/f1000research.9465.1.

    PMID: 27990273
  16. 16

    Risk and clinicopathological features of osteosarcoma metastasis to the lung: A population-based study.

    Huang X, Zhao J, Bai J, et al.

    Journal of bone oncology 2019; (16()):100230 doi:10.1016/j.jbo.2019.100230.

    PMID: 30923668
  17. 17

    Ultrasound-Guided Trans-Uterine Cavity Core Needle Biopsy of Uterine Myometrial Tumors to Differentiate Sarcoma from a Benign Lesion-Description of the Method and Review of the Literature.

    Stukan M, Rutkowski P, Smadja J, Bonvalot S

    Diagnostics (Basel, Switzerland) 2022; (12(6)) doi:10.3390/diagnostics12061348.

    PMID: 35741158
  18. 18

    Percutaneous Core Needle Biopsy Can Efficiently and Safely Diagnose Most Primary Bone Tumors.

    Crenn V, Vezole L, Bouhamama A, et al.

    Diagnostics (Basel, Switzerland) 2021; (11(9)) doi:10.3390/diagnostics11091552.

    PMID: 34573895
  19. 19

    UK guidelines for the management of bone sarcomas.

    Gerrand C, Athanasou N, Brennan B, et al.

    Clinical sarcoma research 2016; (6()):7 doi:10.1186/s13569-016-0047-1.

    PMID: 27148438
  20. 20

    Needle tract seeding of a sclerosing epithelioid fibrosarcoma in a biopsy tract: a case report.

    Kawai M, Miwa S, Yamamoto N, et al.

    BMC musculoskeletal disorders 2023; (24(1)):454 doi:10.1186/s12891-023-06553-0.

    PMID: 37270505
  21. 21

    Does an excision of needle bone biopsy tract affect the prognosis in patients with primary bone tumor?

    Gami A, Shah A, Shankaralingappa S, et al.

    Journal of orthopaedics 2024; (48()):13-19 doi:10.1016/j.jor.2023.11.039.

    PMID: 38059219
  22. 22

    Needle tract seeding after percutaneous biopsy of sarcoma: Risk/benefit considerations.

    Berger-Richardson D, Swallow CJ

    Cancer 2017; (123(4)):560-567 doi:10.1002/cncr.30370.

    PMID: 27859013
  23. 23

    Osteosarcoma.

    Beird HC, Bielack SS, Flanagan AM, et al.

    Nature reviews. Disease primers 2022; (8(1)):77 doi:10.1038/s41572-022-00409-y.

    PMID: 36481668

This page explains osteosarcoma biology and diagnostic procedures for educational purposes. Always consult your pediatric orthopedic oncologist regarding specific diagnostic tests and treatment decisions for your child.

Get notified when new evidence is published on Osteosarcoma.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.