Breast cancer patients who continue to smoke after having radiotherapy run a much higher risk of their treatment giving them lung cancer in the future, research has found.
Two in three of those diagnosed with early breast cancer in the UK given radiotherapy. It is a long-established and highly effective treatment, but also has potential side effects.
Radiotherapy reduces the risk that someone’s breast cancer will recur after treatment and also that they will die from the disease, but its dangers include an increased risk of dying from heart disease, lung cancer or esophageal cancer.
Breast cancer is the UK’s most common cancer, with 56,400 new cases diagnosed each year, almost all of them in women. It kills 11,500 people a year – 32 every day.
The new findings show breast cancer patients who do not smoke have less than a 1% chance of radiotherapy directly leading to them developing lung cancer in the years afterwards. But for those who do smoke when treated and don’t quit afterwards, their risk is between 2% and 6%.
The results are from research in the UK led by Carolyn Taylor, a 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 for treating cancer. In breast cancer, it reduces the chance of the cancer coming back in the future,” said Taylor. “But it is also important to consider the risks. One of the long-term risks of radiotherapy is that it can cause second cancers many years later. This is a rare side effect, but it is important to consider.”
Her study 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 breast, we can’t avoid giving some radiation doses to the surrounding tissues, like the lungs,” she said. “This radiation can damage cells in the lungs.
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“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 years in the future.”
The conclusions of the study, which analyzed 14 previous studies of doses of radiation given to thousands of women with breast cancer in the UK, should be seen as “reassuring” for most women having radiotherapy, Taylor said. This is because most women with breast cancer who can get the treatment are non-smokers, as only 14% of women in the UK smoke. “For them, their risk of lung cancer due to the radiation is less than 1%. So, for them our study is good news”.
However, for long-term smokers who do not kick the habit, “their risks are higher. British breast cancer radiation will increase their risk of lung cancer by between 2% and 6%.”
Deborah Arnott, the chief executive of Action on Smoking and Healthsaid 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 is true for any cancer treated with radiotherapy, not just breast cancer, makes the treatment itself more unpleasant and less effective, with an increased risk of subsequent cancer recurrence.”
Cancer Research UK recently acknowledge smoking as a cause of breast cancer for the first time, along with known risks such as diet and genetics. Labor promised in its general election manifesto to make smoking cessation services available to all hospital patients to encourage more people to quit.
