I was going to link to the Reason piece "WHO Cares? The World Health Organization cares more about its own life than the lives of the poor" because the capture of useful  public health organization by social activists is a fairly universal problem, but this little section on suppressing the science about cancer and second hand smoking is too good to pass up quoting:

In its war on tobacco, WHO has attempted Orwellian moves of almost absurd incompetence. In 1998, for instance, the group was supposed to release an enormous 10-year study on second-hand smoke's links with lung cancer, the largest ever done in Europe. A small mention of it was printed in a WHO report before the whole study was available. The British Sunday Telegraph tried to get a copy of the study, since the brief reference intriguingly implied that it could not find a statistically significant link between second-hand smoke exposure and lung cancer. The Telegraph implied that WHO was trying to bury the report since its results went against their official anti-tobacco stance.

WHO and other anti-tobacco groups were outraged. One group, Action on Smoking and Health, filed an official complaint with Britain's Press Complaints Commission over the supposedly erroneous reporting. (The commission found in the Telegraph's favor.) WHO responded to reports that its study did not find a statistically significant link between second-hand smoke and lung cancer in a press release headlined, "Passive Smoking Does Cause Lung Cancer, Do Not Let Them Fool You" -- strange, strained language from a supposedly scientific organization.

Underneath that colorful headline, the press release states, in italics, that "passive smoking causes lung cancer in non-smokers." Then, in the very next paragraph, it clarifies, "The study found that there was an estimated 16% increased risk of lung cancer among non-smoking spouses of smokers. For workplace exposure the estimated increase in risk was 17%. However, due to small sample size, neither increased risk was statistically significant." In other words, the Telegraph report was exactly correct: The study had found no statistically significant link between second-hand smoke and cancer.

As for the "suppressed" part, WHO insisted that the paper was merely being peer-reviewed, not hidden. Yet three years later, you'll still find no mention of the report on WHO's list of "Comprehensive Reports on Passive Smoking by Authoritative Scientific Bodies."