"Risk of colorectal cancer after initiation of orlistat: matched cohort study"  BMJ
http://www.bmj.com/content/347/bmj.f5039 
"Conclusions
This study found no evidence of an increased risk of colorectal cancer after the initiation of orlistat. It is limited by the relatively short follow-up time, and the possibility of adverse effects of long term orlistat use on risk of colorectal cancer cannot be excluded."