Women diagnosed with early breast cancer are only marginally more likely to develop another compared with the general population.
The risks of a second breast cancer after a previous early breast cancer is low, according to new research in the BMJ.
An analysis of almost half a million women in England over around 20 years found that women who had surgery for an early breast cancer were only 2-3% more likely to develop a second primary breast cancer than women in the general population.
In the 20 years following their surgery, one in seven women developed a non-breast cancer and one in 20 developed a contralateral breast cancer.
These were only 2.1% and 3.1% higher than the general population, respectively. And the risks of contralateral breast cancer diagnoses were higher among younger women compared with older women.
Non-breast cancers were typically womb, lung or bowel cancers, and radiotherapy was tied to more contralateral breast cancers and lung cancers, while endocrine therapy was tied to uterine cancer and a lower rate of contralateral breast cancer, and chemotherapy was tied to acute leukemia.
“Although for cancers of the uterus, soft tissue, bones and joints, and salivary glands, as well as acute leukaemias, standardised incidence ratios exceeded those of the general population by a factor of at least 1.5, absolute excess risks at 20 years were <1% for every individual non-breast cancer type,” the authors wrote.
They said the findings could be used to inform patients of their risks.
“The risks of invasive cancers are higher for breast cancer survivors than for other women in the general population,” the authors wrote.
“These additional risks are small in comparison with the risks of recurrence and death from breast cancer in the great majority of women with diagnosis of early invasive breast cancer despite the substantial falls in breast cancer mortality recently reported.
“This is an important consideration in efforts to reduce morbidity by de-escalating treatments, as it may compromise breast cancer cure.
They noted that lifestyle factors such as smoking and obesity had more of an influence on subsequent diagnoses than a previous breast cancer diagnosis.
Moreover, doctors could give more tailored advice on risk profiles for different demographics.
“For example, for a woman whose index breast cancer was diagnosed when she was aged 60, her risk of developing a new cancer by the age of 80 are 17% for non-breast cancer and 5% for contralateral breast cancer compared with risks of 15% and 3%, respectively, for women of the same age in the general population.
“For a woman with breast cancer diagnosed when she was aged 40, her risks of developing a second invasive cancer by the age of 60 are 6% for both non-breast and contralateral breast cancer compared with 4% and 2%, respectively, for women in the general population.”
This may dispel misconceptions about risks among patients too.
“Our experiences suggest that many patients with breast cancer believe their second cancer risks are much higher than they really are,” wrote several cancer patient advocates in an accompanying editorial.
“This study also shows the importance of taking endocrine therapy, which helps to treat the initial cancer and reduces the risk of a second breast cancer.
“After experiencing breast cancer, people want to understand the benefits of their treatments. It also puts long term risks of treatment into perspective.
“Thinking back to one of the most difficult times in our lives, we believe the findings from this study would have offered us some comfort at the time of diagnosis and later. There is a lot to digest at that time, so not everyone will want all the details then, but it should be there for those who do and for those who seek it later. Information on risks should be readily available.
“It helps us to plan our lives and think ahead to the future.”
