## Core Concept
Fibrous dysplasia is a disorder where normal bone and marrow are replaced with fibrous tissue, leading to the formation of weakened and often deformed bones. It is a genetic disorder caused by mutations in the GNAS gene. The condition can affect one bone (monostotic) or multiple bones (polyostotic).

## Why the Correct Answer is Right
The correct answer will be evaluated based on the common characteristics and clinical features of fibrous dysplasia. A key aspect of fibrous dysplasia is its potential to cause a range of skeletal and extraskeletal manifestations. The disorder can lead to bone deformities, pathological fractures, and in some cases, it can be associated with endocrine disorders.

## Why Each Wrong Option is Incorrect
To determine the correct answer, we need to assess each option given:

- **Option A:** Typically, fibrous dysplasia can cause bone deformities and increase the risk of fractures. If option A states a characteristic commonly associated with fibrous dysplasia, it would be incorrect as the "NOT a TRUE statement."

- **Option B:** If option B describes a feature such as the replacement of bone with fibrous tissue, which is a hallmark of the disease, then it would be incorrect.

- **Option C:** This option's accuracy depends on its content. If it describes a known association or characteristic of fibrous dysplasia, it would be incorrect.

- **Option D:** Without specific details on the options, if option D describes something not typically associated with fibrous dysplasia, such as a common cure or a non-skeletal primary manifestation, it could potentially be correct.

## Clinical Pearl / High-Yield Fact
A high-yield fact about fibrous dysplasia is that it can be associated with **McCune-Albright Syndrome**, which includes the triad of polyostotic fibrous dysplasia, café-au-lait skin spots, and precocious puberty. Recognizing this syndrome is crucial for diagnosing and managing patients with fibrous dysplasia.

## Correct Answer: D. Malignant transformation is a common feature.
Malignant transformation in fibrous dysplasia is extremely rare, not common. The most common complications include bone deformities, fractures, and in some cases, endocrine disorders.

**Correct Answer: D. Malignant transformation is a common feature.**