Background: Emerging data suggest that ovarian cancers differ by tumor grade. However, the reliability of microscopic grade from paraffin tissue in the general medical community and as reflected in population-based cancer registries is unknown.
Methods: We examined grade agreement between two gynecologic pathologists and the Surveillance Epidemiology and End Results Residual Tissue Repository (SEER). Grade agreement was assessed with percent observer agreement and kappa coefficients for 664 invasive ovarian carcinomas, using previously defined three-tier and two-tier grading systems. A random subset of ovarian carcinomas was selected to compare intra- and inter-pathologist agreement.
Results: Five hundred and eighty-six of SEER's 664 tumors were confirmed invasive. Percent agreement was 49 % with fair kappa coefficient = 0.25 (95 % CI: 0.20-0.30) for the 664 tumors. Agreement improved slightly when restricted to the 586 confirmed invasive cancers; it was better for high grade than low grade tumors, for two-tier than three-tier grading systems, and within (66 %) than between study pathologists (43 %). Grade was not a robust independent predictor of ovarian cancer-specific survival.
Conclusions: Grade agreement was fair between SEER and study pathologists irrespective of grading system. Recorded grade in SEER should be used with caution and is probably not a reliable metric for ovarian cancer epidemiology.