and the attrition rate is 5%. Therefore, the total trial size
(2660) will be sufficient to detect a 6% absolute difference
of disease free survival rate for all subjects between
the two treatments, with a two-sided logrank test of 5%
type I error and 90% power; further, our 3-year DFS
rate for colon cancer is assumed to be 65%, which is
similar to the entire group as a whole, the size of colon
cancer (2000) will be sufficient to detect a 6% absolute
difference of disease free survival rate for colon cancer
Dukes C / high risk Dukes B colon cancer or
Rectal cancer subgroups
Complete Surgical Resection of Tumor
Standard adjuvant chemotherapy +
Radiotherapy
Eligible patient
Randomisation
Aspirin
200 mg OD for 3 years
Placebo
200 mg OD for 3 years
3 monthly follow-up for 3 years
followed by
6 monthly follow-up for 2 years
3 monthly follow-up for 3 years
followed by
6 monthly follow-up for 2 years
Figure 1 CONSORT Diagram. OD, once daily.
Ali et al. Trials 2011, 12:261
http://www.trialsjournal.com/content/12/1/261
Page 4 of 8
between the two treatments, with a two-sided logrank
test of 5% type I error and 80% power.