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The table below summarizes the available evidence on the risks and benefits of hormone therapy. Included are all randomized trials and meta-analyses looking at disease incidence or mortality. Inclusion of observational trials was dependent on size: case-control studies with 500 or more cases of the disease and cohort studies with at least 2,000 women are included here.

The year noted is when the study results were published. The name following the title of the study is the last name of the first author on the publication.

E = estrogen; P = progestin

Year	Study	Study Type	Participants	Hormones	Results	Other Notes
1995	MacLennan	Meta-analysis (13 observational)	14 studies	E, E+P	No significant difference in relative risk of colorectal cancer in hormone users	No distinction between E vs. E+P use, or between colon vs. rectal cancer
1996	Persson	Cohort	22,597	E, E + P	Reduction in colon cancer risk by 40% with E + P	No effect with estrogen; 13 years of follow-up
1999	Grodstein (A)	Meta-analysis (17 observational; 1 randomized)	18 studies	E, E+P	Decreases colon cancer risk 20%; decreases rectal cancer risk 19%	No distinction between E vs. E+P use
1999	Nanda	Meta-analysis (24 observational, 1 randomized)	25 studies	E, E+P	33% reduction of risk in recent users (within year of study); ever-use reduced risk 8%	No distinction between E vs. E+P use; rectal cancer not affected by hormone use
2002	Women's Health Initiative	Randomized	16,608	E+P	37% reduction in colon cancer rates	Average follow-up 5.2 years