Most Americans born into the generations that came after the Baby Boom have gone their entire lives aware that smoking can cause lung cancer. But this fact has not always been well-known – and at one time it wasn’t known at all.

Actually, it wasn’t even until cigarettes were mass produced and popularized by manufacturers in the first part of the 20th century that there was cause for alarm. Prior to the 1900s, lung cancer was a rare disease. Turn-of-the-century changes though, gave way to an era of rapidly increasing lung cancer rates. New technology allowed cigarettes to be produced on a large scale, and advertising glamorized smoking. The military got in on it too – giving cigarettes out for free to soldiers during World Wars I and II.

Cigarette smoking increased rapidly through the 1950s, becoming much more widespread. Per capita cigarette consumption soared from 54 per year in 1900, to 4,345 per year in 1963. And, lung cancer went from rarity to more commonplace – by the early 1950s it became “the most common cancer diagnosed in American men,” writes American Cancer Society Chief Medical Officer Otis Brawley, M.D., in an article published November 2013 in CA: A Cancer Journal for Clinicians.

However, though tobacco usage and lung cancer rates increased in tandem, few experts suspected a connection, according to Brawley and his co-authors.

 

The 1950 Turning Point

There were a few small-scale studies conducted from the late 1920s to late 1940s that suggested a possible link between smoking and lung cancer, but these studies had several limitations – and didn’t provide the evidence necessary to establish a clear connection between smoking and lung cancer.

This began to change in the 1950s. Five larger retrospective studies were published in the early 1950’s that again showed a link between cigarette smoking and lung cancer. Though important, these studies still didn’t make a convincing enough case as they relied on the self-reported smoking habits of people who already had lung cancer, and compared them to those who didn’t. One potential problem with this type of study is that people with lung cancer are more likely to overestimate how much they smoked, while those who don’t have lung cancer are more likely to underestimate how much they smoked.

To address this issue, a prospective (cohort) study was needed – recruiting healthy people and following them over time to see who develops or dies from lung cancer and who does not. Without such evidence, the tobacco industry was able to cast doubt on the link between smoking and death from lung cancer and other diseases, says Eric Jacobs, Ph.D., an epidemiologist at the American Cancer Society.

Two American Cancer Society Researchers Get to Work

To address the criticism of the retrospective studies – and to strengthen the evidence that smoking is a cause of lung cancer – E. Cuyler Hammond, Ph.D., and Daniel Horn, Ph.D., scientists working for the American Cancer Society, started work on what is known as a cohort study.

Hammond and Horn 1

In January 1952, Hammond and Horn engaged 22,000 American Cancer Society volunteers to help recruit a large group of American men aged 50 to 69 across 10 U.S. states and ask these men about their smoking habits. The scientists ended up with a cohort of about 188,000 men, who they eventually followed through 1955.

The participants were asked whether they smoked cigarettes, if they did smoke how often they smoked, and how many cigarettes they smoked. They were asked about both their current and past smoking habits. The questionnaire also asked about cigar and pipe smoking.

In November 1952, the volunteers began the first follow up. Each volunteer was in charge of 5 to 10 men. When the volunteer researchers followed up with their participants, they were required to check on the questionnaire whether the man was “alive,” “dead,” or “don’t know.” Hammond and Horn then obtained copies of the official death certificates of all the men who died to confirm their cause of death.

‘Cause and Effect Relationships’

After following the men for about 20 months, Hammond and Horn had enough information to publish what they called “preliminary” findings in an August 7, 1954 Journal of the American Medical Association article. Their conclusion was clear: “It was found that men with a history of regular cigarette smoking have a considerably higher death rate than men who have never smoked or men who have smoked only cigars or pipes,” the researchers wrote.

Hammond and Horn noted that the higher death rate in smokers was due primarily to heart disease and cancer. “Deaths from cancer were definitely associated with regular cigarette smoking.” They called out lung cancer in particular: “The death rate from lung cancer was much higher among men with a history of regular cigarette smoking than among men who never smoked regularly.”

Hammond and Horn 2

Dr. E. Cuyler Hammond (left), Dr. Daniel Horn (center), and American Cancer Society Medical and Scientific Director Dr. Charles Cameron (right) at the 1954 American Medical Association conference.

These two researchers finally felt they had the convincing evidence that cigarette smoking was a cause of lung cancer that the world was previously lacking. They ended their 1954 paper stating “… we are of the opinion that the associations found between regular cigarette smoking and death rates from diseases of the coronary arteries and between regular cigarette smoking and death rates from lung cancer reflect cause and effect relationships.”

Hammond and Horn were so convinced by these findings that they had presented them a couple months earlier, in June of 1954, at the American Medical Association’s annual conference. Previously heavy cigarette smokers, Hammond and Horn changed to pipes by the time of the meeting (although they later concluded that pipe smoking was also cancer causing).

Hammond and Horn’s results were uniquely important at the time, says Susan Gapstur, Ph.D., vice president of the American Cancer Society’s epidemiology research program. “Their study – along with the British Doctor’s study conducted around the same time – were the first two large prospective studies to establish a link between smoking and the subsequent risk of death from lung cancer and other diseases.”

An Even Bigger Study and a Letter to President Kennedy

After his success with the first cohort study, Hammond and the American Cancer Society in 1959 started a larger and more robust long-term follow-up study, called Cancer Prevention Study I (CPS-I). This time, 68,000 volunteers, across 25 states, recruited more than 1 million men and women.

The data Hammond collected through this study provided further conclusive evidence about the harmful effects of smoking and were a major contributor to the landmark 1964 Surgeon General’s Report on Smoking and Health. That report led to sweeping tobacco policy changes in the United States and played a significant role in curbing smoking throughout the nation.

The creation of that landscape-altering report began with a letter sent to President John F. Kennedy in June 1961. In it, leaders from the American Cancer Society, the American Public Health Association, and the National Tuberculosis Association urged Kennedy to form a national commission on smoking to find “a solution to this health problem …” Kennedy asked his surgeon general, Luther Terry, to tackle this.

Terry formed an advisory committee to study the available evidence on smoking and health. Over the course of more than a year, the members analyzed 16 independent studies, conducted in 5 different countries, over a period of 18 years.

“The principal data on the death rates of smokers of various types and of nonsmokers come from 7 large prospective studies of men,” according to the 1964 surgeon general’s report. These studies, when combined, consisted of data from 1,123,000 men, more than half of whom came from the American Cancer Society’s Hammond-Horn Study and Cancer Prevention Study-I.

Terry published the final report January 11, 1964 – 50 years ago. It concluded that: “Cigarette smoking is a health hazard of sufficient importance in the United States to warrant appropriate remedial action.”

That strong judgment fueled stop-smoking efforts across the United States. And since that time, the U.S. smoking rate has dropped by more than half.

Though it took many years after smoking started to decline for the lung cancer death rate to begin to come down, over time, it did – dramatically so for men. In men, lung cancer death rates have declined about 34% from their peak in 1990. In women, lung cancer death rates did not begin to decrease until 2003 because women started smoking in large numbers about 2 decades later than men. The lung cancer death rate among women is now 9% less than it was at its peak in 2002 and is expected to continue declining.

Questions Yet to Answer About Smoking and Health

Although progress has been made, millions of Americans still smoke – and die from – cigarettes. To review the strides the U.S. has made over the past 50 years and provide a call to action for what is left to be done to address tobacco use, the surgeon general will publish a new report on smoking and health in late January.

The report draws on the research that the American Cancer Society and others have continued to do since the time of Hammond and Horn. “The importance of continuing to document the high number of deaths due to cigarettes cannot be overestimated,” says Gapstur, whose team continues to conduct large long-term follow-up studies in the U.S.

Additionally, not every question about the effects of smoking on health has been answered yet. Gapstur and Jacobs say that questions remain about issues such as: exposure to secondhand smoke, particularly in childhood; the effects of e-cigarettes on smoking initiation and cessation; and which former smokers are at high enough risk to benefit from lung cancer screening.

As researchers continue to study smoking and health, additional anti-tobacco efforts are still needed, according to Tom Glynn, Ph.D., director of international cancer control for the American Cancer Society. “Nearly half a million Americans and 6 million people worldwide will die from tobacco use in 2014 – but we know what to do to stop that,” Glynn says.

He calls for implementing the World Health Organization’s global tobacco treaty, continuing to raise taxes on tobacco products, making smoke-free environments the norm rather than the exception, and ensuring science-based tobacco dependence treatment is available to everyone who wants to stop using tobacco. Glynn also wants “to encourage every country to develop the political and financial will to eliminate tobacco as a source of health and economic disruption.”
 

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