Architectural patterns: In high-grade serous carcinomas of the ovary, papillary growth is usually the predominant pattern and is at least focally present. The papillae are architecturally complex, show hierarchical branching, have true fibrovascular cores and are lined by pseudostratified tumor cells. Other growth patterns include glandular, cribriform, cystic, microcystic, solid, and transitional cell carcinoma-like. Stromal invasion (not shown here) by isolated tumor cells, small clusters, or nests is seen accompanied by desmoplastic response. Cytologic features: The tumor cells have high-grade features, including marked nuclear pleomorphism, high nucleus:cytoplasm ratio, hyperchromasia, one or more prominent nucleoli, and increased mitotic activity (often > 30 mitoses/10 HPF). Psammoma bodies are frequently seen.