**Core Concept**
Malignant transformation of osteochondroma, most commonly into chondrosarcoma, is characterized by progressive changes in the lesion’s growth pattern and local symptoms. These signs reflect underlying tissue degeneration and tumor progression, with specific features indicating a shift from benign to malignant behavior.

**Why the Correct Answer is Right**
Weight loss is not a typical or specific sign of malignant transformation in osteochondroma. While pain, increased size, and thickening of the cartilage cap are all recognized warning signs—due to local pressure, necrosis, or invasive growth—weight loss is a systemic symptom associated with malignancy in general, not specifically with osteochondroma progression. The thickening of the cartilage cap and increasing size reflect active tumor growth, which are key indicators of transformation.

**Why Each Wrong Option is Incorrect**
Option A: Pain indicates active growth or necrosis and is a classic early sign of malignant change in osteochondroma.
Option C: Increase in size signifies progressive tumor growth, a hallmark of malignant transformation.
Option D: Thickening of the cartilage cap reflects abnormal cartilage proliferation, a pathological feature of chondrosarcoma development.

**Clinical Pearl / High-Yield Fact**
In osteochondroma, **persistent pain, rapid growth, and cartilage cap thickening** are red flags for malignant transformation; **weight loss is not a specific or common feature** and should not be considered a primary indicator.

✓ Correct Answer: B. Weight loss