Background: Most published series of ovarian carcinoma find a correlation between histologic grade and survival, but the grading system used commonly is not specified, and several different systems exist, some of which use different criteria for different histologic types. However, several studies have shown marked interobserver variability in distinguishing among the histologic types of ovarian carcinoma. The authors attempted to derive a universal grading system for all invasive ovarian carcinomas (IOC), based on the Nottingham system for grading all types of mammary carcinoma.
Methods: The authors studied 461 patients with IOC of different histologic types and clinicopathologic stages who were treated in a uniform manner between 1980 and 1994 with surgery and cisplatin-based chemotherapy. All slides were reviewed and the tumors graded as follows: Architectural pattern (predominant): Glandular = 1, Papillary = 2, and Solid = 3; Nuclear pleomorphism: Slight = 1, Moderate = 2, and Marked = 3; Mitotic activity (mitotic figures per 10 high-power fields [1 HPF = 0.345 mm2]) in most active region: 0-9 = 1, 10-24 = 2, and > or = 25 = 3; Grade 1 = total score (adding three values obtained earlier) 3-5, Grade 2 = 6 or 7, and Grade 3 = 8 or 9.
Results: Tumor grade correlated with survival in both early and advanced stage disease and for all major histologic types of IOC except clear cell carcinoma (CCC). Results for CCC approached but did not reach clinical significance. By multivariate analysis, only this tumor grade and performance status were significant in Stage I/II IOC. For Stage III/IV tumors, the new tumor grade also was significant, as were performance status, residual tumor size, response to chemotherapy, and mucinous (unfavorable) or transitional cell (favorable) histologic type. International Federation of Gynecology and Obstetrics grade (based primarily on architectural features) did not correlate significantly with survival except in Stage III/IV serous and Stage I/II mucinous carcinomas.
Conclusions: The new grading system reported is simple, reproducible (among the current study authors), and useful for all histologic types and clinical stages of IOC. Further testing for reproducibility and clinical utility is recommended.