By Kerry Grens
NEW YORK (Reuters Health) - Across eight European and Scandinavian countries, 270,000 people are diagnosed every year with cancers caused by smoking, according to a new study.
"These results tell us that (the) contribution of tobacco smoking to cancer is substantial, and that, in spite of substantial efforts put forward to reduce smoking in European countries, the overwhelming importance of cigarette smoking on cancer risk is still of public health concern, and a priority from the point of view of prevention," said Dr. Antonio Agudo, the lead author of the study and a researcher at the Catalan Institute of Oncology in L'Hospitalet de Llobregat, Spain.
Smoking is known to be a major contributor to a variety of cancers, including lung, colon and bladder cancers.
Understanding just how great the burden of smoking is on cancer rates is important to developing prevention strategies, Agudo wrote in an email to Reuters Health.
He and his colleagues, as part of the European Prospective Investigation into Cancer and Nutrition (EPIC), gathered information on more than 440,000 residents of Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain, Sweden and the United Kingdom.
One out of four men and one out of five women in the study currently smoked. A slightly larger proportion - about one of every three men and roughly one out of every four women - had smoked previously.
The researchers began tracking the participants, none of whom had been diagnosed with cancer at the beginning of the study, between 1992 and 2000.
Over an average of 11 years of follow up, the team found that 14,563 people who were exposed to tobacco smoke developed a type of cancer that is considered to be fully or partly caused by tobacco exposure. This is equivalent to 270 diagnoses out of every 100,000 people.
Current smokers were 2.6 times as likely as never smokers to develop a tobacco-related cancer and ex-smokers had 1.5 times the risk.
Nearly 4,500 people were diagnosed with colon or rectal cancer, about 3,000 with lung cancer and 1,850 people developed lower urinary tract cancer.
Other types of tobacco-related cancers were less common, but included stomach, cervix, mouth, kidney, pancreas and a form of leukemia.
Although each of these cancers has been associated with smoking, not all of the cases were caused by it.
The researchers calculated the "attributable fraction," or the proportion of cancer cases likely to blame on cigarettes, and determined that overall 35 percent were caused by smoking.
For some types of cancers - such as lung and larynx - the vast majority, more than 80 percent, were caused by smoking, whereas a smaller portion of others, including kidney cancers (eight percent) and pancreas cancers (13 percent), were caused by smoking.
Agudo's study, published in the Journal of Clinical Oncology, included only a sample - although a relatively young and healthy one - of the European population.
Across the eight countries with data available for both men and women, about 1.5 million new cancer cases are diagnosed each year - half of the tobacco related forms of cancer, according to the researchers.
Given the proportion of those attributable to smoking, the group calculated that 270,000 cancer cases each year in those countries are due to cigarettes.
The number "is not far from our expectations," said Agudo.
Dr. Prabhat Jha, a professor at the University of Toronto who was not involved in the study, said the findings are consistent with estimates of how many deaths are caused by smoking in Europe.
He added that the numbers could be underestimates, however.
Jha pointed out that the researchers found the risk of developing lung cancer among women to be about a third that of men, but that could be because the women were not followed long enough.
"The main reason might be that the full effects of smoking on cancer in the specific women studied in EPIC have not yet matured," he told Reuters Health in an email.
Jha noted that in wealthy countries, such as those in Europe in North America, the rates of smoking-related cancers and deaths have declined substantially, while cancer rates in China and India are rising.
Nevertheless, "this study should support greater EU efforts" to curb smoking, he said.
Agudo added, "our results come from a group of countries where efforts to reduce tobacco smoking are already in place since long ago. Thus we hope they can (be) useful as well to countries where the tobacco epidemic is still increasing to enhance efforts to face this serious health threat."
SOURCE: http://bit.ly/Ve0y5o Journal of Clinical Oncology, online November 19, 2012.