**Core Concept**
Paget's disease is a chronic bone disorder characterized by abnormal bone remodeling, leading to deformities and an increased risk of complications, including malignant transformation. This condition affects the skeletal system, causing an imbalance in bone resorption and formation, resulting in bone weakness and an increased risk of secondary bone cancers.

**Why the Correct Answer is Right**
The correct answer is B. Osteosarcoma, as Paget's disease increases the risk of osteosarcoma, a type of bone cancer that originates from osteoid tissue. This is due to the abnormal bone remodeling process, which can lead to the formation of malignant cells. The risk of osteosarcoma is significantly higher in patients with Paget's disease, especially in the skull and long bones.

**Why Each Wrong Option is Incorrect**
* **Option A:** Osteoma is a benign bone tumor that is not directly associated with Paget's disease. While osteoma can occur in the skull, it is not a complication of Paget's disease.
* **Option C:** Fibrosarcoma is a rare type of cancer that originates from fibrous tissue, but it is not a common complication of Paget's disease. The risk of fibrosarcoma is not significantly increased in patients with Paget's disease.
* **Option D:** The correct answer is only B. Osteosarcoma, and not all options listed. Therefore, option D is incorrect.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize the increased risk of osteosarcoma in patients with Paget's disease, especially in the skull and long bones. A high index of suspicion is required for early detection and treatment of osteosarcoma in these patients.

**Correct Answer:**
✓ Correct Answer: B. Osteosarcoma