Research has shown that breast cancer patients who continue to smoke after undergoing radiation therapy have a much greater risk that their treatment will cause lung cancer in the future.
Two out of three people with early breast cancer in the UK receive radiotherapy. It is a long-standing and highly effective treatment, but it also carries potential side effects.
Radiation therapy reduces the risk of a person’s breast cancer coming back after treatment and also of dying from the disease. However, its dangers include a higher risk of dying from heart disease or lung cancer or esophageal cancer.
Breast cancer is the most common cancer in the UK, with 56,400 new cases diagnosed each year, almost all of them women. It kills 11,500 people a year – 32 a day.
The new findings show that breast cancer patients who don’t smoke have less than a 1% chance that radiation therapy will directly lead to lung cancer in the years afterward. But for those who smoke when they’re treated and don’t quit, their risk is between 2% and 6%.
The findings come from research led by Carolyn Taylor, professor of oncology at the University of Oxford, which was funded by Cancer Research UK and published in the journal Clinical Oncology.
“Radiotherapy is very good at treating cancer. In breast cancer, it reduces the chance of the cancer coming back in the future,” Taylor said.
“But it’s also important to consider the risks. One of the long-term risks of radiotherapy is that it can cause second cancers after many years. This is a rare side effect, but it’s important to consider.”
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Her research is the first of its kind to be conducted in the UK. “The reason radiotherapy can cause a second cancer is because when we give a dose to the chest, we can’t avoid also giving a dose of radiation to the surrounding tissues, such as the lungs,” she added. “That radiation can damage cells in the lungs.
“Radiotherapy damages the DNA in cells. Damage to the DNA in cancer cells can kill them. This reduces the chance of the cancer coming back. But it can also damage the DNA in some normal cells, and this damage to normal cells can rarely cause cancer in the future.”
But the conclusions of the study, which analysed 14 previous studies of radiation doses given to thousands of women with breast cancer in the UK, should be seen as “reassuring” for most women undergoing radiotherapy, Taylor added.
That’s because most women with breast cancer who can have the treatment are non-smokers, with only 14% of women in the UK smoking. “For them, their risk of developing lung cancer from the radiation is less than 1%. So our study is good news for them.”
However, for people who have smoked for a long time and have not stopped smoking, the risks are higher. British breast cancer radiotherapy is said to increase their risk of lung cancer by 2% to 6%.
Deborah Arnott, director of Action on Smoking and Health, said smokers undergoing radiotherapy “should be warned of the risks of continuing to smoke and given the support and encouragement they need to quit.
“Continuing to smoke, and this applies to all cancers treated with radiotherapy, not just breast cancer, makes the treatment itself more unpleasant and less effective, with an increased risk of the cancer returning later.”
Cancer Research UK recently recognized smoking has been listed for the first time as a cause of breast cancer, alongside known risks such as diet and genetics. Labour pledged in its general election manifesto to make smoking cessation services available to all hospital patients, to encourage more people to quit.