Reproducibility of tumor measurements in ovarian cancer: a study of interobserver variability

We evaluated the accuracy and interobserver variability of intraoperative tumor measurements in ovarian cancer. Thirty-four obstetrician-gynecologists, 26 gynecologic oncologists, and 12 residents estimated the size of a primary ovarian cancer and four metastases in a simulated patient at laparotomy. The validity of the model was rated from 1 (poor) to 10 (excellent) as 6.9 +/- 1.3 (range 4-10). Actual diameters and range of estimates were, respectively, primary ovarian tumor, 13 cm and 4 to 20 cm; plaque right pelvic sidewall, 8.5 cm and 0 to 12 cm; paraaortic nodes, 2 cm and 0 to 5 cm; right hemidiaphragm, 1 cm and 0.3 to 3 cm; and left hemidiaphragm, 5 cm and 2 to 7 cm. There was no significant difference in measurements between the three groups of surgeons. More surgeons underestimated than overestimated tumor diameters. Tumor measurements in individual patients are highly variable; interpretation of the surgical literature and ovarian cancer treatment protocols based on tumor volume are subject to significant measurement error.