Women who have had early breast cancer have a lower risk of developing a second cancer than previously thought
A new study by researchers at Oxford Population Health has found that women who have been successfully treated for early invasive breast cancer have a lower risk of developing a second primary cancer than previously thought. The study is published in The BMJ.
Breast cancer survivors have an increased risk of developing a second primary cancer. Second primary cancers are new, separate cancers that are not the result of the original breast cancer spreading. The methods used to calculate women’s risk of second primary cancers in the past have been inconsistent and previous studies have reported varying associations between early breast cancer and the risk of a second primary cancer.
In this study, researchers looked at diagnosis and treatment data recorded in England’s national cancer registry for 475,000 women aged between 20 and 75 who were diagnosed with early invasive breast cancer between 1993 and 2016. They then looked at the records for these women up until the end of October 2021 to determine whether any of them had been diagnosed with a second cancer.
This information was used to calculate the chance that a woman with early breast cancer would develop a second primary cancer and also the chance that a woman of similar age in the general population would develop a primary cancer. This enabled the researchers to determine which factors, including the age that a woman had a diagnosis of early breast cancer and the treatment she received, may influence future cancer risks.
Key findings:
- By 20 years after the original breast cancer diagnosis, 13.6% of the women studied had developed a second primary non-breast cancer, only 2.1% more than the general population.
- In the same period, 5.6% of the women with early breast cancer had developed a second primary cancer in the other unaffected breast (contralateral breast cancer) 3.1% more than expected in the general population
- The risk of developing a second primary non-breast cancer was higher for women who were older when they were diagnosed with their original breast cancer and for women living in more deprived areas. Women who lived in more deprived areas were also more likely to develop cancers known to be more common in smokers.
- For second primary non-breast cancers, the 20-year absolute excess risk was mostly from womb (non-cervix) and lung cancers. For all other cancer types, these excess risks were less than 0.2%.
- For women who were diagnosed with a second primary cancer in their other breast, the risk was higher for women who were younger when they were diagnosed, had larger tumours, whose original cancer was diagnosed in earlier calendar years, was of a type called lobular cancer (which can be harder to detect), or was oestrogen-receptor negative;
- When looking at risks associated with treatments the women had received for their original cancer, around 2% of all second primary cancers were associated with radiotherapy, hormone therapy, or chemotherapy.
Dr David Dodwell, Senior Clinical Research Fellow at Oxford Population Health and consultant clinical oncologist, said ‘Our study confirms that the risks of new cancers are higher for breast cancer survivors than for other women in the general population. However, these additional risks are small in comparison to the risks of recurrence and breast cancer death in the great majority of women diagnosed with early invasive breast cancer, despite the substantial improvements in the treatment of early breast cancer recently reported.
‘The risks reported in this study can inform breast cancer patients and the clinicians who treat and support them. For example, for a woman whose original breast cancer was diagnosed when aged 60, her risks of developing a new cancer by the age of 80 are 17% for non-breast cancer and 5% for contralateral breast cancer, compared to risks of 15% and 3% respectively for women of the same age in the general population.
‘For a woman diagnosed when aged 40, her risks of developing a second primary cancer by the age of 60 years, are 6% for both non-breast and contralateral breast cancer compared to 4% and 2% respectively for women in the general population. As described in the accompanying patient perspective, many breast cancer survivors believe their second cancer risks are much higher than those we estimated. The information in our study can reassure them and help them to plan their future.’
Caroline Geraghty, senior specialist information nurse at Cancer Research UK, said ‘This research should provide some reassurance to women who have had early invasive breast cancer. We’ve known for a while that having breast cancer increases a person’s chance of developing a different, unrelated cancer but until now we haven’t known how much higher this chance was. These findings, that the risk is only marginally higher, are very promising.
However, if women who have had early breast cancer are ever concerned, they should speak to their doctor. They know their body best, so if they spot something that’s not right, their doctor will want to hear from them.’
The data collected from this study has been used to create a new online tool that enables users to look at risk calculations for second cancers after an early breast cancer diagnosis.
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