A binary histologic grading system for ovarian serous carcinoma is an independent prognostic factor: A population-based study of 4317 women diagnosed in Denmark 1978-2006

Objective: To evaluate the prognostic significance of histologic grade on survival of ovarian serous cancer in Denmark during nearly 30 years. Methods: Using the nationwide Danish Pathology Data Bank, we evaluated 4317 women with ovarian serous carcinoma in 1978-2006. All pathology reports were scrutinized and tumors classified as either low-grade serous carcinomas (LGSC) or high-grade serous carcinomas (HGSC). Tumors in which the original pathology reports were described as well-differentiated were classified as LGSC, and those that were described as moderately or poorly differentiated were classified as HGSC. We obtained histologic slides from the pathology departments for women with a diagnosis of well-differentiated serous carcinoma during 1997-2006, which were then reviewed by expert gynecologic pathologists. Data were analyzed using Kaplan-Meier methods and Cox proportional hazards regression analysis with follow-up through June 2009. Results: Women with HGSC had a significantly increased risk of dying (HR = 1.9; 95% CI: 1.6-2.3) compared with women with LGSC while adjusting for age and stage. Expert review of 171 women originally classified as well-differentiated in 1997-2006 were interpreted as LGSC in 30% of cases, whereas 12% were interpreted as HGSC and 50% as serous borderline ovarian tumors (SBT). Compared with women with confirmed LGSC, women with SBT at review had a significantly lower risk of dying (HR = 0.5; 95% CI: 0.22-0.99), and women with HGSC at review had a non-significantly increased risk of dying (HR = 1.6; 95% CI: 0.7-3.4). Conclusions: A binary grading system is a significant predictor of survival for ovarian serous carcinoma.