Okudela K, Woo T, Saigusa Y, et al. - Since the Ki‐67 index is used to evaluate proliferative activity, which is a strong prognostic factor in lung adenocarcinoma (LADC), researchers sought to optimize the measurement the Ki‐67 index and verify the best cut‐off value. Employing different antibodies, MIB1 and SP6, 342 LADCs at stage I were analyzed for the immunohistochemical expression of Ki‐67. The tumor was evenly subdivided into 0.25 mm² tiles. In each tile of an invasive area or the whole tumor, experts counted frequency of positive cells. They computed the number of tumor cells needed to generate a 95% confidential interval (CI) < 0.05. By counting 2,000 cells from 10 random tiles (200 cells each) in invasive areas, the goal could be met. Researchers discovered that by using an SP6 antibody, an optimal procedure was successfully achieved, which afforded coverage probabilities > 70% and CI of < 0.05 in over 90% of cases. Also, experts found an optimal cut‐off value of 0.12 with an alternative of 0.15, on the basis of disease recurrence, and suggested the utility of both this procedure and the cut‐off values in the routine pathological diagnosis of LADC.