**Core Concept**
Uterine sarcomas are a rare and malignant type of tumor that arises from the smooth muscle or connective tissue of the uterus. They are distinct from more common types of uterine cancer, such as endometrial adenocarcinoma.

**Why the Correct Answer is Right**
Uterine sarcomas account for approximately 5% of all malignant uterine tumors. This is because they are relatively rare compared to other types of uterine cancer. The majority of uterine cancers are endometrial adenocarcinomas, which arise from the glandular epithelium of the endometrium. In contrast, uterine sarcomas originate from the smooth muscle or connective tissue of the uterus. The rarity of uterine sarcomas is due to the low frequency of mutations that lead to their development.

**Why Each Wrong Option is Incorrect**
**Option B:** 10% is incorrect because it overestimates the prevalence of uterine sarcomas. While uterine sarcomas are a significant concern due to their aggressive nature, they are not as common as other types of uterine cancer.

**Option C:** 15% is incorrect because it further overestimates the prevalence of uterine sarcomas. Uterine sarcomas are a rare occurrence, and 15% would represent a significant portion of all uterine cancers.

**Option D:** 20% is incorrect because it is a substantial overestimation of the prevalence of uterine sarcomas. Uterine sarcomas are a rare type of cancer, and 20% would be an unrealistic representation of their frequency.

**Clinical Pearl / High-Yield Fact**
It is essential for gynecologists and obstetricians to be aware of the rarity of uterine sarcomas and to consider them in the differential diagnosis of patients presenting with uterine tumors. A high index of suspicion is necessary to diagnose uterine sarcomas, as they can mimic other types of uterine cancer.

**✓ Correct Answer: A. 5**