Most common malignant tumour of bone is:
Osteosarcoma typically occurs in adolescents and young adults, often in the metaphysis of long bones like the femur or tibia. It's a high-grade sarcoma that forms osteoid. Other options like Ewing's sarcoma are also malignant but less common. Chondrosarcoma is more common in older adults and arises from cartilage. Fibrosarcoma is rare. So the correct answer should be osteosarcoma.
Now, for the core concept, I need to state that osteosarcoma is the most common primary malignant bone tumor, emphasizing its demographics and location. Then explain why it's correct, mentioning the age group, location, and histology. For the wrong options, each one has different reasons: Ewing's is more common in children but less than osteosarcoma, chondrosarcoma is in older people, and fibrosarcoma is rare.
The clinical pearl should highlight that osteosarcoma is the most common in young adults and Ewing's in children. Also, metastasis patterns might be important. Finally, make sure the correct answer is clearly marked and the explanation is concise but covers all necessary points without exceeding the character limit.
**Core Concept**
The most common primary malignant bone tumor is **osteosarcoma**, which predominantly affects adolescents and young adults. It arises from mesenchymal cells and is characterized by the formation of malignant osteoid. This tumor typically occurs in the metaphysis of long bones, such as the distal femur or proximal tibia.
**Why the Correct Answer is Right**
Osteosarcoma accounts for approximately 35–40% of all primary bone sarcomas. It is associated with mutations in tumor suppressor genes like *TP53* and *RB1*, leading to uncontrolled proliferation of osteoblast-like cells. The tumor produces osteoid (bone-like matrix) that can be identified histologically. Its peak incidence during skeletal growth spurts (adolescence) is linked to rapid bone remodeling. Metastasis commonly occurs via the bloodstream to the lungs.
**Why Each Wrong Option is Incorrect**
**Option A: Ewing’s sarcoma** – While it is a common bone tumor in children, it is less frequent than osteosarcoma and typically affects the diaphysis of bones.
**Option B: Chondrosarcoma** – This arises from cartilage and is more common in older adults, not the most prevalent in general.
**Option C: Fibrosarcoma** – A rare bone tumor, usually occurring in the jaw or as a secondary lesion.
**Clinical Pearl / High-Yield Fact**
Remember the "ABC" of primary bone tumors: **O**steosarcoma is the **O** (most common), followed by **E**wing’s sarcoma in **E**arly childhood, and **C**hondrosarcoma in **C**ommon older adults. Osteosarcoma’s association with bone growth and its characteristic osteoid production are key diagnostic clues.