Many social smokers believe they don’t puff on enough cigarettes to be at risk of serious side effects.
But new research shows that smoking just 100 cigarettes in a lifetime increases a woman’s chance of developing breast cancer by 30 per cent.
The research also revealed that women between 20 and 44 years old who have smoked a pack of cigarettes a day for at least 10 years are 60 per cent more likely to develop the most common form of breast cancer.
Dr Christopher Li, from the Fred Hutchinson Cancer Research Centre in Seattle, and his team analysed data from young women in the Greater Seattle area who were diagnosed with breast cancer between 2004 and 2010.
Of those women, 778 were diagnosed with the more common oestrogen receptor-positive type and 182 had the less common but more aggressive triple-negative type.
The researchers also included information from 938 cancer-free women for comparison.
‘I think there is growing evidence that breast cancer is another health hazard associated with smoking,’ said Dr Li.
According to the National Cancer Institute, about one in every eight American women will eventually develop breast cancer – but the risk is lower at younger ages.
Only about one in every 227 30-year-old women will develop breast cancer before the age of 40, for example.
In this study, young women who had smoked were about 30 per cent more likely to develop any type of breast cancer, compared to women who had never smoked.
The researchers defined ‘never having smoked’ as having smoked fewer than 100 cigarettes.
So, anyone who had smoked more than 100 in their lifetime counted as a smoker.
When the researchers looked at each type of breast cancer separately, there was no link between smoking and triple-negative breast cancer.
But women who were recent or current smokers – and had smoked for at least 15 years – were about 50 per cent more likely to have oestrogen receptor-positive breast cancer, compared to women who had smoked for fewer years.
And those women who reported smoking at least one pack a day for 10 years were 60 per cent more likely to have that type of cancer, compared to lighter smokers.
It could be that some of the substances found in cigarettes act like oestrogens, which would promote oestrogen receptor-positive breast cancer, the researchers write.
‘There are so many different chemicals in cigarette smoke that can have so many kinds of effects,’ Dr Li said.