**Core Concept**
Serous cystadenoma of the ovary is a type of benign epithelial tumor, characterized by the proliferation of serous-lined cysts. These tumors arise from the ovarian surface epithelium, which is the layer of cells covering the surface of the ovary.

**Why the Correct Answer is Right**
Serous cystadenomas typically present as large, unilocular or multilocular cysts, often filled with clear or yellowish fluid. They are usually unilateral and can vary in size. The tumor cells are characterized by their columnar or cuboidal morphology, with moderate nuclear atypia. The pathogenesis of serous cystadenomas is thought to involve genetic mutations affecting the Wnt/β-catenin signaling pathway, leading to uncontrolled cell growth and tumor formation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because serous cystadenomas are typically benign and do not metastasize. They may, however, undergo malignant transformation into serous cystadenocarcinoma in a small percentage of cases.
**Option B:** This option is incorrect because serous cystadenomas are not usually associated with a significant increase in CA-125 levels. Elevated CA-125 levels are more commonly seen in ovarian cancers, such as serous cystadenocarcinoma.
**Option C:** This option is incorrect because serous cystadenomas can be bilateral in a small percentage of cases, but this is not a characteristic feature of the tumor.

**Clinical Pearl / High-Yield Fact**
It is essential to distinguish serous cystadenomas from other ovarian tumors, such as serous cystadenocarcinoma, which can present with similar clinical features but have a much worse prognosis.

**Correct Answer: D.**