**Question:** Giant cell tumor is seen at -

A. Endocrine system
B. Central nervous system
C. Musculoskeletal system
D. Respiratory system

**Core Concept:**
Giant cell tumor (GCT) is a benign, locally aggressive tumor originating from the chondrocytes or bone-forming cells. It is characterized by the presence of multinucleated giant cells and is classified into three subtypes: conventional, cellular, and osteoblastic.

**Why the Correct Answer is Right:**
Giant cell tumor primarily occurs in the skeletal system, specifically affecting the epiphysis of long bones. It is more common in middle-aged adults, with a slight female predominance. The correct answer (C) represents the correct anatomical location for GCT: the musculoskeletal system.

**Why Each Wrong Option is Incorrect:**
A. The endocrine system includes the glands and hormones, not bone-forming cells or giant cell tumors.
B. The central nervous system consists of the brain and spinal cord, not giant cell tumors or bone-forming cells.
D. The respiratory system includes the lungs and respiratory tract, which do not involve bone-forming cells or giant cell tumors.

**Clinical Pearl:**
Giant cell tumors are often misdiagnosed as osteoid osteoma or osteoblastoma, two other benign bone tumors. However, GCT typically presents as a solitary, circumscribed mass with a well-defined margin, while osteoid osteoma often exhibits symptoms at night and is smaller. Histopathological examination helps differentiate these entities.

**Correct Answer:** C. Musculoskeletal system