**Core Concept**
The question pertains to endometrial cancer, specifically focusing on identifying a subtype with a poor prognosis. Endometrial cancer arises from the endometrium, the lining of the uterus, and is classified into various subtypes based on histological characteristics and molecular markers.

**Why the Correct Answer is Right**
Endometrial cancer is primarily classified into two main types: Type I and Type II. Type I endometrial cancers are the most common and are characterized by estrogen receptor positivity and low-grade histology. In contrast, Type II endometrial cancers are aggressive, often lacking estrogen receptor expression, and are associated with a poor prognosis. They are further sub-classified into serous and clear cell carcinomas, with serous carcinoma being particularly aggressive.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the subtype of endometrial cancer with a poor prognosis. While some endometrial cancers may have a poor prognosis, this option lacks clarity.
* **Option B:** This option might be a distractor, but it is not a specific subtype of endometrial cancer with a poor prognosis. It may refer to a treatment or management approach, but it does not directly address the question.
* **Option C:** This option could be a distractor, but it is not a known subtype of endometrial cancer with a poor prognosis. It may refer to a symptom or presentation of endometrial cancer, but it does not directly address the question.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize that endometrial cancer with a poor prognosis often lacks estrogen receptor expression and is characterized by high-grade histology and aggressive behavior. This knowledge can guide clinical decision-making and treatment planning.

**Correct Answer:** C. Serous carcinoma