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 downloading the pdf by clicking here , going to the pdf download link and then looking at pages 219-311.
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
6. References
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.
Coming Home 
This is extremely helpful! I searched for a long time for a few of those links at the top, but didn’t find the second link. Thank you for posting this.
[…] {UPDATE 2/15/12: It seems that WHO has taken down the page. However, they have made several expanded pages with a wealth of data. Click here for the links. […]
I am full of questions, rhetorical in nature, based on the information you make available in this post:
Why are women constantly misled in this regard?
Why are women so easily convinced to risk their health for sexual gratification and/or interference with their fertility cycles, when the reality is that there are links to cancer — and mastectomy is no fun, neither is chemo/radiation therapy for the treatment of any cancer?
And the medical community, — “first do no harm” in the Hippocratic Oath — shouldn’t they be more concerned about the fact that for very few people this medication constitutes a NEED, but are prescribed this medication as an elective drug vs. a required medication; and the fact that the risks far outweigh, in the majority of cases, the actual benefit when there are other more reliable methods available that do not cause cancer and are also morally acceptable (NFP — NAPRO Technology)?
The science is clear, or, I assume, it would not be included in this list, so why is it not more prominently presented by the foremost provider of contraceptives (and abortion — also linked to breast cancer), Planned Parenthood? Perhaps because it doesn’t fit their business model (or diabolical philosophy)?
Women’s health? Really? And, made available for ALL to see by the World Health Organization?
Is agent another word for ingredients?
Lena,
In a manner of speaking, yes. They can also be stand-alone entities, like plutonium.
[…] Comments « World Health Organization Data on Birth Control Pill and Estrogen Replacement Carcinogenicity […]
Kathy: The answer to your question? Money.
Thank you for this excellent explanation. I’ve linked to it on my FB page and will add to my blog where I’ve been looking at the published warnings that come with contraceptive tools and pills.
[…] of the talk about women’s health, I have never heard anyone discuss why a drug that has been classified as a group 1 carcinogen (carcinogenic to humans) by the World Health Organization is good for women’s health. […]
Thank you for updating the links: very useful!