**Core Concept**
Malignant transformation in a lipoma, particularly in the retroperitoneum, involves the development of a **liposarcoma**, a type of cancer that arises from fat cells. This process is associated with genetic mutations and can lead to significant clinical implications. The retroperitoneal space is a common location for lipomas to occur.

**Why the Correct Answer is Right**
The correct answer is related to the clinical presentation of liposarcoma. A key feature of malignant transformation in a retroperitoneal lipoma is the potential for the tumor to grow significantly and cause symptoms due to its size and location, such as abdominal pain or a palpable mass.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not directly relate to the common presentations of liposarcoma.
**Option B:** Similarly, this option does not accurately describe the typical symptoms associated with malignant change in a retroperitoneal lipoma.
**Option C:** This choice is also incorrect as it does not align with the expected clinical findings in liposarcoma.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that liposarcomas can present with non-specific symptoms, making diagnosis challenging. A high index of suspicion is necessary, especially in the context of a growing retroperitoneal mass.

**Correct Answer:** D. Abdominal pain or a palpable mass.