The reproducibility of histological parameters employed in the novel binary grading systems of endometrial cancer

Objective: To compare the interobserver reproducibility and prognostic value of the FIGO grading system with the histological parameters employed in the various recently proposed binary grading systems of endometrial cancer. Methods: Seventy two consecutive stage I endometrioid endometrial carcinomas from hysterectomy specimens were independently graded by two pathologists. Clinical data and outcome were obtained from the patients' records. The following histological parameters were evaluated: FIGO grade (dichotomized to grades 1and 2 vs. grade 3), nuclear atypia, presence of more than 50% solid growth, diffusely infiltrative rather than expansive growth pattern, presence of tumor cell necrosis, and mitotic count. Interobserver agreement was measured by the kappa (k) statistics. Kaplan-Meier survival analysis, log-rank tests and Cox proportional hazard regression were used to evaluate the equality of survival distributions and to model the overall effects of the various predictor variables on survival. Results: The interobserver reproducibility was as follows: FIGO grade, k = 0.65; nuclear atypia, k = 0.63; solid growth, k = 0.51; infiltrative growth pattern, k = 0.38; tumor necrosis, k = 0.52; and mitotic index, k = 0.44. In the comparison of the Kaplan-Meier curves, the following parameters were associated with a significantly poorer survival: FIGO grade 3, p = 0.02; presence of more than 50% solid growth, p = 0.01; and a high mitotic index, p = 0.01. The other binary histological parameters were not significantly predictive of survival. Conclusions: The proposed novel binary grading parameters are not advantageous in terms of interobserver reproducibility and prognostic significance over dichotomization to FIGO grades 1 and 2 vs. grade 3. A simple binary grade based solely on presence of more than 50% solid growth has a comparable reproducibility and prognostic value.