**Core Concept**
The question is testing the student's knowledge of primary bone tumors, specifically those that exhibit neural differentiation. The correct answer requires an understanding of the histopathological characteristics of bone cancers.

**Why the Correct Answer is Right**
The boy's symptoms and biopsy results suggest a primary bone tumor with neural differentiation, which points towards Ewing's Sarcoma. Ewing's Sarcoma is a malignant bone tumor that arises from the primitive neuroectodermal cells of the bone. It is characterized by the presence of small, round, blue cells with a high nuclear-to-cytoplasmic ratio, which are indicative of neural differentiation. The tumor also exhibits aggressive features such as bone destruction and soft tissue mass, consistent with the radiologist's report.

**Why Each Wrong Option is Incorrect**
**Option A:** Osteosarcoma is a primary bone tumor that exhibits osteoid production, not neural differentiation. It is the most common primary bone tumor in children and adolescents, but it does not match the boy's biopsy results.

**Option B:** Chondrosarcoma is a malignant cartilage tumor that does not exhibit neural differentiation. It is more common in adults and is characterized by the presence of cartilage matrix in the tumor.

**Option C:** Fibrosarcoma is a malignant fibrous tumor that does not exhibit neural differentiation. It is more common in adults and is characterized by the presence of spindle-shaped cells in a fibrous stroma.

**Option D:** Lymphoma is a malignant tumor of the immune system that can present in the bone, but it does not typically exhibit neural differentiation.

**Clinical Pearl / High-Yield Fact**
Ewing's Sarcoma is a highly aggressive bone tumor that requires prompt treatment. It is characterized by a high rate of metastasis to distant sites, including the lungs, bones, and bone marrow.

**Correct Answer: D. Ewing's Sarcoma**