Reliability of quantitating proliferative cell nuclear antigen in epithelial ovarian tumors

Sources of variability in quantitating proliferative cell nuclear antigen (PCNA) by image analysis were evaluated in paraffin sections of 18 ovarian tumors of low malignant potential (LMP) and grade 1 (G1) carcinomas. The correlation coefficient of reliability (R) was calculated to determine how reliable a single observation was for representing a "true" tumor value. Reliability of 61% was obtained when interobserver and intraobserver variability were assessed. Threshold settings for positive nuclear and antibody signals minimally affected the overall reliability. The reliability of a single block of tumor for representing true tumor value was R = 0.61. These sources of variability render this technique impractical for evaluating proliferative characteristics in LMP and G1 common epithelial ovarian tumors with PCNA staining.