A 62-year-old postmenopausal woman from Delhi presents with progressive abdominal distension and mild abdominal pain for 3 months. She reports early satiety and occasional nausea. On examination, there is abdominal distension with shifting dullness. Pelvic ultrasound reveals a large complex cystic and solid mass arising from the right ovary, measuring 12 cm, with internal septations and solid nodules. CA-125 is markedly elevated at 480 U/mL. Staging CT shows ascites and peritoneal involvement. What is the most likely histological diagnosis?

Explanation

## Clinical Presentation and Diagnosis This case describes a postmenopausal woman with a large, complex ovarian mass, elevated CA-125, and advanced-stage disease with ascites and peritoneal involvement—classic features of **serous cystadenocarcinoma**. ### Key Distinguishing Features **Key Point:** Serous cystadenocarcinoma is the most common malignant epithelial ovarian tumor, accounting for ~40% of epithelial ovarian cancers. | Feature | Serous | Mucinous | Clear Cell | Endometrioid | |---------|--------|----------|-----------|---------------| | **Frequency** | 40% of EOC | 10% of EOC | 10% of EOC | 10% of EOC | | **Age** | 50–70 years | 40–60 years | 40–50 years | 40–50 years | | **CA-125** | Markedly elevated | Mildly elevated; CEA elevated | Mildly elevated | Mildly elevated | | **Stage at diagnosis** | Often advanced (III–IV) | Often early (I–II) | Often early (I–II) | Often early (I–II) | | **Ascites** | Common | Rare | Uncommon | Uncommon | | **Peritoneal involvement** | Frequent | Rare | Rare | Rare | | **Gross appearance** | Cystic with solid areas, papillae | Multilocular, gelatinous | Solid, tan-yellow | Solid, tan-white | | **Microscopy** | Ciliated cuboidal epithelium | Tall columnar mucin-secreting cells | Clear cytoplasm, hobnail cells | Resembles endometrial cancer | ### Why Serous Cystadenocarcinoma Fits This Case 1. **Age and presentation:** Postmenopausal woman with insidious onset abdominal symptoms—typical for serous tumors. 2. **Markedly elevated CA-125 (480 U/mL):** Serous tumors are the most prolific CA-125 producers; mucinous tumors typically show only mild elevation and elevated CEA instead. 3. **Advanced stage with ascites and peritoneal involvement:** Serous cystadenocarcinomas have a propensity for peritoneal dissemination and are frequently diagnosed at stage III–IV, whereas mucinous, clear cell, and endometrioid tumors are usually caught at early stages. 4. **Complex cystic-solid mass with internal septations:** Consistent with serous cystadenocarcinoma; mucinous tumors are typically multilocular and gelatinous without prominent solid nodules. ### Microscopic Findings **Clinical Pearl:** Serous cystadenocarcinomas show ciliated cuboidal epithelium with high-grade nuclear atypia, increased mitotic activity, and invasion through the capsule. The presence of psammoma bodies (concentric calcifications) is a characteristic but not specific finding. **High-Yield:** Serous tumors are more aggressive than mucinous tumors and have worse prognosis; they respond better to platinum-based chemotherapy but are more likely to present at advanced stage. ### Prognosis and Management **Key Point:** Stage III–IV serous cystadenocarcinomas require aggressive cytoreductive surgery followed by platinum-taxane chemotherapy. Five-year survival for stage III disease is ~40%, compared to ~90% for stage I disease. [cite:Robbins 10e Ch 22]