Ohashi R, Martignoni G, Hartmann A, et al. - In this study, the presence of sarcomatoid differentiation, necrosis, and mitosis was investigated in a Swiss cohort (n = 42), an Italian cohort (n = 103), a German cohort (n = 54), a Japanese cohort (n = 119), and The Cancer Genome Atlas cohort (n = 64) in order to validate formerly proposed three-tiered chromophobe grading system. In univariate analysis, all three histological parameters were significantly related to a shorter time to tumor progression and overall survival. High concordance for the classification of sarcomatoid differentiation and tumor necrosis yet only low to medium concordance for the identification of mitosis were exhibited by interobserver variability for recognition of these parameters. In multivariate analysis, the pT stage, individual's age, lymph node and/or distant metastasis, and the two-tiered grading system were notably related to overall survival and were individualistic prognostic parameters. Thus, this multi-institutional assessment of prognostic parameters implied that of a two-tiered chromophobe tumor grading system, tumor necrosis and sarcomatoid differentiation as reproducible components.