Childhood osteosarcoma: the bone cancer that changed our story forever

There are illnesses that are explained to you and you understand them. And there are illnesses that shatter your life, and only then do you grasp what they truly mean. Osteosarcoma is one of those. We know because Adán lived it, because his family lived it, and because that experience bound us together forever in a single mission: that no family should ever face this diagnosis alone.

At Asociación Adán González Muñoz, osteosarcoma is not an abstract concept. It is the reason we exist.

What is osteosarcoma?

Osteosarcoma is a malignant bone tumour that originates in osteoblastic cells — the cells responsible for forming new bone. It is the most common primary bone cancer in childhood and adolescence, and tends to appear during periods of rapid growth, when bones are most active.

Unlike other childhood cancers that can be picked up through routine blood tests, osteosarcoma usually presents with pain — a pain that is often mistaken for growing pains, sports injuries, or ordinary childhood bumps. That confusion can delay the diagnosis by weeks or months.

Key facts about osteosarcoma

• It accounts for roughly 3–5% of all childhood cancers
• Around 60–80 new cases are diagnosed each year in Spain in children under 20
• The peak incidence is between ages 10 and 25, coinciding with the pubertal growth spurt
• It is slightly more common in boys than in girls
• The most frequent sites are the area around the knee (distal femur and proximal tibia) and the proximal humerus (shoulder)
• Five-year survival in localised osteosarcoma is 60–70%
• In metastatic osteosarcoma, survival drops to 20–30%

What are the symptoms?

The symptoms of osteosarcoma are deceptively ordinary, which makes early suspicion difficult:

• Persistent pain in a bone or joint, especially around the knee, thigh or shoulder
• Localised swelling or lump over the affected bone
• Limping or difficulty moving the limb
• Pain that worsens at night or with physical activity
• Pathological fractures: the bone, weakened by the tumour, breaks from a minor impact
• In advanced stages: fatigue, weight loss, difficulty breathing (if pulmonary metastases are present)

The greatest danger with osteosarcoma is confusing it with “growing pains.” If your child complains of persistent bone pain that does not improve with rest, always consult the paediatrician and request an X-ray.

How is it diagnosed?

Diagnosing osteosarcoma follows a sequence of tests:

1. Plain X-ray: usually the first test that raises suspicion. The typical pattern shows bone destruction with new bone formation (“sunburst” pattern or “Codman’s triangle”)
2. MRI scan: essential for determining the local extent of the tumour and planning surgery
3. Chest CT: to rule out pulmonary metastases, present in 15–20% of cases at diagnosis
4. Bone scintigraphy: to detect whether other bones are involved
5. Biopsy: confirms the histological diagnosis. It must be performed by a team specialised in bone tumours
6. Blood tests: elevated alkaline phosphatase and LDH can provide clues, though they are not specific

How is osteosarcoma treated?

The standard treatment for osteosarcoma combines chemotherapy and surgery in a protocol lasting 9 to 12 months:

Phase 1: Neoadjuvant chemotherapy (before surgery)

• Usually lasts 10–12 weeks
• Uses a combination of drugs: high-dose methotrexate, doxorubicin and cisplatin (MAP protocol)
• Dual objective: shrink the tumour and eliminate possible micro-metastases

Phase 2: Surgery

• Limb-salvage surgery in 80–90% of cases: the tumour is removed while preserving the limb using a prosthesis or bone graft
• Amputation only when it is not possible to save the limb with safe margins
• The histological response to chemotherapy is analysed: if more than 90% of the tumour is necrotic, the prognosis is significantly better

Phase 3: Adjuvant chemotherapy (after surgery)

• Treatment continues with the same drugs for an additional 12–18 weeks
• If the response was good (>90% necrosis), the MAP protocol is maintained
• If the response was poor (<90% necrosis), some centres add drugs such as ifosfamide and etoposide

What research owes us — and what we can do

Osteosarcoma is one of the cancers where research has stalled most painfully. The same drugs used in the 1980s remain the backbone of current treatment. In four decades, survival has barely improved. This is not acceptable.

The most promising lines of research include:

• Immunotherapy: monoclonal antibodies targeting proteins found on osteosarcoma cells (such as GD2 or HER2)
• Tyrosine kinase inhibitors: drugs that block the tumour’s growth signals (regorafenib, cabozantinib)
• CAR-T cell therapy: genetically modifying the patient’s own immune cells to attack the tumour
• mTOR pathway-targeted treatments: such as everolimus, which curbs cell proliferation
• Gene therapy: identifying and attacking each tumour’s specific mutations to offer personalised treatments

At Asociación Adán González Muñoz, every euro we raise goes directly to funding these lines of research at leading institutions such as Hospital Vall d’Hebron in Barcelona and IRB Barcelona (Institute for Research in Biomedicine), with whom we actively collaborate. Because we know that research is not a luxury — it is the only real hope.

The story that drives us

Adán González Muñoz is not a name on a statistic. He is the boy whose smile taught us that life is worth fighting for with everything you have, that hospitals can also be places where you play, and that the love of a family can move mountains.

Osteosarcoma took him, but it could not take what he left behind: a community that refuses to forget, that organises tournaments, that raises funds, that demands louder every day that research advances so other children can have the chance that Adán did not.

If you are reading this because you have just received an osteosarcoma diagnosis for your child — breathe. You are not alone. Write to us. We are here.

How can you help?

• Donate to our association — remember that donations are tax-deductible up to 80% on the first €150 on your Spanish tax return
• Take part in the Adán González Muñoz Tournament 2026, where every entry funds research
• Share this article — the more people who learn about osteosarcoma, the sooner the funding that research needs will arrive
• Contact us if your family is going through this: contacto@asociacionadangonzalezmunoz.org

Together, for Adán and for every child fighting bone cancer.

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This article is for informational purposes only and does not replace professional medical advice. If you have concerns about your child’s health, always consult their oncologist or bone tumour specialist.