OSTEOSARCOMA.
Definition.
Osteosarcoma is a malignant tumor of the bone mesenchyma in which the cancerous cells produce bone matrix. In OSTEOSARCOMA the proliferating spindle cell stroma directly produces osteoid or immature bone. This tumor is the most common primary malignant bone tumor.
Etiology.
The actual cause is not known but as with other human cancers genetic, environmental conditions such as irradiations and chemicals, and other factors like the presence of primary bone lesion such as Paget’s disease and retinoblastoma are known predisposing factors.
Pathogenesis.
Tumor tissue involves the entire width of the medullary cavity; infiltrating and replacing the marrow surrounding the pre-existing trabeculae bone. The tumor erodes and penetrates the cortex, and lifts up the peritoneum and extends into the neighboring soft tissues.Infrequently; they penetrate the epiphyseal plate or enter the joint.
Occurrence in a person.
- Primary osteosarcoma occurs in young ages of not more than 20 years.
- Males are more affected than females.
- Most common sites/location is the knee area (i.e. distal femur and proximal tibia).Other sites that may be affected include the pelvis, proximal femur, proximal humerus, mandible, maxillary bones and nasal bone.
- In secondary osteosarcoma the most common locations are those sites with primary bone disease.
Classes/groups of osteosarcoma
- Primary osteosarcoma that arises naturally irrespective of the pre-existing bone disease. Primary ostosarcoma accounts about 80% of osteosarcomas.
- Secondary osteosarcoma which is due to pre-existing bone disease such as
Ø Bone cyst or fibrous dysplasia in young age.
Ø Paget’s disease in adults over the age of 40.
Depending on the anatomic portion of the bone from which the tumors arise, there are three subtypes of osteosarcoma.
· Intramedullary-the most common.
· Intracortical. Osteosarcoma
· Surface (Parosteal and Periosteal) osteosarcoma.
Clinical symptoms.
- Painful progressive enlargement of the affected bone.
- Sometimes (although uncommon) pathologic fracture may be the first symptom.
- The duration of symptom is generally short, varying from weeks to several months.
Clinical signs.
- A tender mass generally is palpable on physical examination since soft tissue extension is common.
- When the mass is very large, dilated and engorged blood vessel (veins) may be seen overlying it.
- Increased serum alkaline phosphatase is common.
- Edema distal to the lesion due to blockage of lymphatics or venous compression sometimes although is uncommon.
Gross pathological features.
- Typical OSA is composed of gritty, bulky, gray-white mass which involve the entire width of the medullary canal, cortex and neighboring soft tissues. The tumor is often hemorrhagic and has cystic degeneration
- Necrosis (dead tissue) is mostly seen.
Microscopic features.