Trial Size Based on our own and other previous data1,2,4, we assumed the development of CIN of 15% in NAC, 15 % in SOB and 5 % in COM. A group sample size of 210 patients would be required to detect a statistically significant difference with a power of 90% and two-tailed test size of 5% between COM and either of SOB or NAC; giving a total of 630 patients