Women with hormone-sensitive breast cancer (oestrogen and progesterone) had triple the risk if they had been exposed to PAHs from petroleum sources.
PAHs are a group of more than 100 different chemicals formed during the incomplete burning of coal, oil and gas, rubbish or other organic substances such as tobacco.
People can be at risk if they breathe in PAHs in workplaces such as coking, coal-tar and asphalt production plants.
Of the women in the study, 556 were diagnosed with breast cancer in 1996/97 in Montreal, Canada, when aged between 50 and 75.
The other 613 women, who were matched for age and date of diagnosis, had a range of other cancers and acted as a comparison group.
The researchers analysed the data while taking into account other factors linked to an increased risk of breast cancer.
They said their findings could be due to chance alone but are consistent with the theory that breast tissue is more sensitive to harmful chemicals if exposure occurs when breast cells are still active — before a woman reaches her 40s.
\[Emily Lea\]As the authors recognise, i\[Emily Lea\]He said the findings were particularly prone to chance because the research started with about 300 agents.
Toxicologist professor Anthony Dayan said: “The conclusions are presented too strongly in relation to the weight of evidence.”
He said it was unclear if all factors had been properly taken into account, including smoking and taking the Pill, both of which are linked to breast cancer.</>