**Core Concept:**

The question is testing the understanding of the occurrence of malignant (cancerous) changes in leiomyomas, benign smooth muscle tumors that are commonly found in the uterus (myoma/leiomyoma). These tumors are derived from the smooth muscle cells of the uterine wall.

**Why the Correct Answer is Right:**

The correct answer, **C. 0.001%**, refers to the extremely rare incidence of malignant leiomyoma. Leiomyomas rarely undergo malignant change, which is also known as uterine sarcoma, specifically, Uterine Leiomyosarcoma (ULMS). ULMS is a rare and aggressive malignancy that develops from the smooth muscle cells of the uterus. The development of ULMS is estimated to occur in less than 1% of all leiomyomas.

**Why Each Wrong Option is Incorrect:**

A. **0.1%:** This option is incorrect because it is significantly higher than the correct answer (0.001%). Malignant change is extremely rare, and a 0.1% figure would not accurately reflect the actual occurrence.

B. **10%:** This option is incorrect as malignant change is extremely rare, and a figure of 10% would be highly exaggerated and not reflect the actual occurrence.

D. **No malignant change:** This option is incorrect because it contradicts the actual fact that malignant change does occur in some leiomyomas, albeit very rarely.

**Clinical Pearl:**

Understanding the rarity of malignant change in leiomyomas is crucial for clinical practice, as it helps in formulating appropriate management strategies and expectations for patients with these tumors. In clinical practice, if a patient presents with a rapidly growing uterine mass or other concerning symptoms, a thorough workup should be performed to rule out sarcomas, including ULMS. Early diagnosis and management are essential to improve patient outcomes, as these tumors have a worse prognosis compared to benign leiomyomas.

**Correct Answer:** C. 0.001%

**Explanation:**

Uterine leiomyomas, also known as fibroids, are common benign tumors in women of reproductive age. The actual incidence of malignant change in these tumors is extremely low, estimated to be around 0.001%. This low rate is due to the fact that benign smooth muscle cells, which make up uterine leiomyomas, do not have the genetic mutations that lead to sarcoma development.

**Why the Other Options are Incorrect:**

A. A higher percentage (0.1%) would significantly overestimate the incidence of malignant change in uterine leiomyomas. The actual incidence is much lower than 10% as it is primarily a benign condition.

B. The statement "No malignant change" is incorrect as malignant change does occur in uterine leiomyomas, albeit extremely rarely.

D. As mentioned earlier, the actual incidence is much lower than 90%, indicating the rarity of malignant change in uterine leiomyomas.

**Clinical Significance:**

Understanding the rarity of malignant change in uterine