Stopping smoking leaves postmenopausal women at a lower risk of bladder cancer than those who continue to smoke, new research confirms.
The greatest reduction in risk versus ongoing smoking was seen in the first 10 years after quitting, according to the study by scientists at Indiana University in the US.
Postmenopausal former smokers’ risk continued to decline versus ongoing smokers after that time, but failed to reach the same level as those who had never smoked even more than 30 years after quitting.
Smoking is the largest known risk factor for bladder cancer. But Dr Yueyao Li, who led the study, said evidence on how risk might change over time after stopping smoking was “inconsistent”.
This research, said Li, highlights how “even those who have smoked for many years stand to benefit from quitting”.
Cancer risk greatest in smokers
The research analysed data from the Women’s Health Initiative, a long-running US-wide study of postmenopausal women which included smoking habits data from 143,279 participants.
Half (52.4%) identified as ‘never smokers’, 40.2% as ‘former smokers’ and 7.1% as ‘current smokers’, when the study started in the 1990s.
By the most recent follow-up in 2017, 870 cases of bladder cancer were identified in the study group. And former smokers were found to be around two-and-a-half times as likely to be diagnosed with bladder cancer compared with those who had never smoked.
Current smokers, meanwhile, were found to have more than three times the risk of developing the disease.
Among the postmenopausal US women in this study, ex-smokers who quit 30 or more years ago were still around twice as likely to be diagnosed with bladder cancer compared with those who had never smoked.
Cancer Research UK’s statistical information and risk manager, Dr Katrina Brown, said the research adds to our existing knowledge on the differences in bladder cancer risk between smokers and non-smokers.
“This US study confirms that while the difference in bladder cancer risk between postmenopausal women who used to smoke and those who never smoked reduces over time, it probably never disappears completely,” she said.
Li said the findings reinforce that the best way to prevent cancer is by never smoking, but that quitting could still bring benefits for postmenopausal women.
The research found that the steepest reduction in bladder cancer risk compared with ongoing smoking occurred in the first 10 years after quitting, a 25% drop.
But analysis shows that although risk continues to decline after this 10-year period, a difference in risk between those who quit and those who have never smoked remains. Brown said ex-smokers probably never completely lose the additional risk of cancer created by their past habit, but the gap between never-smokers and ex-smokers shrinks as the never-smokers’ risk increases simply because they’re getting older.
The study is based on postmenopausal women in the US, so the results may not translate to other groups. Smoking status was also provided by the people taking part in the study and so may be subject to error, and some other key bladder cancer risk factors (like exposure to ionising radiation and certain substances in the workplace) were not taken into account.
But Brown, and the researchers behind the study, said that the data show how important stopping smoking can be for all ages.
“This study reinforces that no matter how old you are, and how long or how heavily you’ve smoked, it’s always a good idea to stop smoking,” said Brown.
Li, Y. et al. (2019) Smoking Cessation and the Risk of Bladder Cancer among Postmenopausal Women. Cancer Prevention Research. doi: 10.1158/1940-6207.CAPR-18-0441.