Lung cancer is the commonest form of the disease, with 2.5 million people diagnosed in 2022, said the study, published in the Lancet Respiratory Medicine journal on World Cancer Day.

Most of them were men but there was a growing share of nearly a million cases among women.

One key subtype of lung cancer -- adenocarcinoma -- has become predominant among women in 185 countries, the authors wrote in the Chinese-funded study.

"Air pollution can be considered an important factor that partly explains the emerging predominance of adenocarcinoma that accounts for 53-70 percent of cases of lung cancer among people who have never smoked worldwide," the study said.

They found it grew among both men and women from 2020 to 2022, with the highest level among women, where it accounted for around six in 10 cases.

"As smoking prevalence continues to decline in many countries worldwide, the proportion of lung cancer in people who have never smoked has increased," the researchers added.

"Lung cancer in people who have never smoked is estimated to be the fifth leading cause of cancer-related mortality worldwide, occurring almost exclusively as adenocarcinoma and most commonly in women and Asian populations."

The study presented statistical research based on data from monitors including the World Health Organization.

The researchers said the highest levels of adenocarcinoma linked to air pollution were detected in east Asia, particularly China.

"Exposure to household burning of solid fuels for heating and cooking could be a causal factor of lung cancer" among Chinese women non-smokers, they added.