In eight European and Scandinavian countries, 270,000 people are diagnosed every year with cancers caused by smoking, according to a European study.
Smoking is known to be a major contributor to a variety of cancers, including lung, colon and bladder cancers, and understanding how great the burden of smoking is on cancer rates is important for developing prevention strategies, said Antonio Agudo, the lead author of the 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 Agudo, a researcher at the Catalan Institute of Oncology in L'Hospitalet de Llobregat, Spain.
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.
The researchers, whose findings appeared in the Journal of Clinical Oncology, began tracking the participants between 1992 and 2000. None had been diagnosed with cancer.
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 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 like as those who had never smoked 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 with lower urinary tract cancer. Other types of tobacco-related cancers were less common but included stomach, cervix, mouth, kidney, pancreas and a form of leukaemia.
Although each of these cancers has been associated with smoking, not all of the cases were caused by it.
35% of various cancer cases can be blamed on smoking
The researchers calculated the "attributable fraction," or the proportion of cancer cases likely blamed on cigarettes, and determined that, overall, 35% were caused by smoking.
For some types of cancers, such as lung and larynx, the vast majority - more than 80% - were caused by smoking. A smaller proportion of others, such as kidney cancers at 8% and pancreatic cancers at 13%, were caused by smoking.
Across the eight countries with data available on both men and women, about 1.5 million new cancer cases are diagnosed each year - half of them tobacco-related.
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 - a number that Agudo said was "not far from our expectations."
Prabhat Jha, a professor at the University of Toronto who was not involved in the study, said the results should support greater EU efforts to curb smoking.