The long-term risk of women diagnosed with early breast cancer developing a second primary cancer is low, new research indicates.
Findings from a large-scale study of English women with the disease will provide reassurance for patients, its authors say.
The study published in the British Medical Journal shows women with an early breast cancer diagnosis have about a 2-3 per cent greater chance of developing a second cancer than women in the general population.
While known that breast cancer survivors were at greater risk, estimates of the risk were inconsistent across previous studies.
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To address this uncertainty, researchers used data from 476,373 women diagnosed with early invasive breast cancer in England between 1993 and 2016. The study included women aged 20-75 years who were treated with surgery.
During this period, 64,747 women developed a second primary cancer, but the risk difference between those who had breast cancer and the general population was found to be small.
Development of a non-breast cancer, mainly womb, lung or bowel cancer, was seen in 13.6 per cent of women – 2.1 per cent more than expected in the general population.
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Contralateral breast cancer (on the other side of the body) developed in 5.6 per cent of cases, 3.1 per cent more than expected.
For a woman whose first breast cancer was diagnosed when aged 60, her estimated risks of developing a new cancer by 80 are 17 per cent for non-breast cancer and 5 per cent for contralateral breast. This drops 2 per cent in both cases for women of the same age in the general population.
With a diagnosis aged 40, a woman’s estimated risks of developing a second cancer by the age of 60 are 6 per cent for both non-breast and contralateral breast cancer compared with 4 per cent and 2 per cent respectively for women in the general population.
Radiotherapy was associated with higher rates of contralateral breast and lung cancers, endocrine therapy with uterine cancer, and chemotherapy with acute leukaemia.
Researchers estimated that about 7 per cent of excess second cancers may be due to the use of such adjuvant therapies, but note that their benefits outweigh this small risk in almost all circumstances where these treatments are recommended.
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The study’s findings may be affected by incomplete cancer registry data for some variables. Other limitations included a lack of data on family history, genetic predisposition and lifestyle choices such as smoking.
However, this research provides a detailed and accurate picture of second cancer development in a complete population of women with early breast cancer for up to 20 years.
The authors say their analyses can “reliably inform breast cancer patients and the clinicians who treat and support them”.
They add that the results are relevant to clinical practice and policy, and may help inform the design of future studies to assess cancer risk.
