There has been confusion of late concerning the World Health Organization’s International Agency for Research on Cancer (IARC) listing for their Group 1 Carcinogens, including several forms of oral contraceptives and estrogen replacement therapy. The confusion has arisen because the original link by WHO has been changed. After some sleuthing, here is a treasure trove of information from WHO. Let’s take the links one at a time.
First are the IARC Group Classifications for agents and their degrees of carcinogenicity:
Group 1 Carcinogenic to humans (107 agents)
Group 2A Probably carcinogenic to humans (59 agents)
Group 2B Possibly carcinogenic to humans (267 agents)
Group 3 Not classifiable as to its carcinogenicity to humans (508 agents)
Group 4 Probably not carcinogenic to humans (1 agent)
The definitions of these groups may be found in the IARC Monograph Preamble on the Evaluation of Carcinogenic Risks to Humans. Click here.
The page with links to the agents by various classification schemes may be found here.
The actual list of all agents, (IN Group number order) beginning with the following known (Group 1) carcinogens containing:
Estrogen therapy, postmenopausal
Estrogen-progestogen menopausal therapy (combined)
Estrogen-progestogen oral contraceptives
may be found by clicking here.
The same estrogens may be found on the list that lists them in alphabetical order with Group number next to their name. Click here.
Going much, much deeper…
There is another link that shows the monographs on:
1. Exposure Data
2. Studies of Cancer in Humans
3. Studies of Cancer in Experimental Animals
4. Other Data Relevant to an Evaluation of Carcinogenicity and its Mechanisms
5. Summary of Data Reported and Evaluation
for each of the following:
Oral Contraceptives, combined
Hormonal Contraceptives, Progestogens Only
Post-Menopausal Estrogen Therapy
Post-Menopausal Estrogen-Progestogen Therapy
The link to this page (which contains all the links to the monographs) may be found here.
Hopefully, this helps. Contrary to rumor, WHO did not hide the data, but actually expanded it in new links. Remember that even small increases in risk when multiplied by hundreds of millions of women taking these drugs will produce large absolute new cases of breast cancer.
P.S. Here is a monograph on all of the known carcinogens: Click here.