The number of lung cancer cases in the Chinese capital Beijing has soared over the last decade.
According to figures published by the state-run Xinhua news agency, they have increased by more than 50%.
Beijing health officials say smoking is still the number one cause of lung cancer, but they admit air pollution is also a factor.
The World Health Organization (WHO) recently estimated that polluted air kills millions of people every year.
Pollution kills millions
Xinhua said the latest figures - which are for only one city and one disease - were issued by Beijing municipal health bureau.
They show the number of lung cancer patients per 100,000 people was 39.56 in 2002, but had jumped to 63.09 by 2011.
The article gave no reason for the increase in patients.
Beijing health officials said lung cancer was linked to lifestyle choices, with smoking still the top cause. But they said passive smoking and air pollution could also be a factor.
Last month the WHO issued a scientific report detailing the link between air pollution and a number of different diseases and illness.
It estimated that breathing in fine particles contributed to 3.2 million premature deaths a year across the world and killed more than 200,000 from lung cancer.
"More than half of the lung cancer deaths attributable to ambient fine particles were projected to have been in China and other East Asian countries," said the WHO.
Correspondents say Chinese people are becoming increasingly worried about the health problems caused by the thick air pollution that often blankets much of their country, a result of rapid economic expansion coupled with poorly enforced laws designed to protect the environment.
Earlier this week it was reported that a eight-year-old girl in Jiangsu province had become the country's youngest lung cancer patient. Air pollution was blamed.
The hospital that was supposed to be treating her denied the reports, but the outcry caused by the story shows just how concerned people have become.