Pilot studies using data from the OEDTR (OEsterreichische Dialysis and Transplant Registry) were conducted to estimate the eGFR decline and variance of sequential eGFR determinations. When using only one eGFR determination at two years as primary endpoint, analyses showed an impracticable high sample size number under the assumption of a median treatment effect of Bortezomib (0.5 SD). Therefore, the difference in slope of half yearly determined eGFR between the two treatment groups will be used as quantitative outcomes measure. Mixed linear models for longitudinal data were used for analyses. Power calculation using an autoregressive covariance matrix of the first order using a correlation of 0.9, an alpha of 0.05 for the interaction term of treatment and time and an attrition of 8% per year showed that 2 x 22 subjects would be required to uncover a difference in GFR slopes of 5ml/min/year with a power of 80%.