Risk of second cancer after early breast cancer only slightly higher than average
Around 14% of women who had early invasive breast cancer developed a non-breast cancer after 20 years, 2.1% more than expected in the general population, an observational study found.
The risk of a second cancer in women treated for early invasive breast cancer is only slightly higher than for women in the general population, according to an observational study of more than 476,000 women in the United Kingdom.
To better understand the long-term risk of second non-breast primary cancer and contralateral breast cancer in women with early invasive breast cancer treated with surgery, researchers assessed data from the National Cancer Registration and Analysis Service for England. A total of 476,373 women were included, all of whom had breast cancer between January 1993 to December 2016. Women were followed until October 2021. Findings were published by The BMJ on August 27.
A total of 64,747 women developed a second primary cancer. At 20 years of follow-up, 13.6% (95% CI, 13.5% to 13.7%) of women had developed non-breast cancer, 2.1% (95% CI, 2.0% to 2.3%) more than expected in the general population. A contralateral breast cancer developed in 5.6% (95% CI, 5.5% to 5.6%), 3.1% (95% CI, 3.0% to 3.2%) more than expected. The 20-year absolute excess risk for contralateral breast cancer with a first cancer was higher in younger women (6.9% vs. 1.3% in women ages 20 to 39 years, 6.0% vs. 2.2% in women ages 40 to 49 years, 5.9% vs. 2.7% in women ages 50 to 59 years, and 5.0% vs. 2.7% in women ages 60 to 69 years).
Among types of non-breast cancer, the largest absolute excess risks were for uterine (0.74%) and lung cancer (0.41%). For all other cancer types, the 20-year cumulative absolute excess risk was 0.2% or lower. However, for cancer of the uterus, soft tissue, bones and joints, and salivary glands and for acute leukemia, standardized incidence ratios exceeded those of the general population by a factor of at least 1.5. Radiotherapy was associated with increased contralateral breast and lung cancer, endocrine therapy with increased uterine cancer (but reduced contralateral breast cancer), and chemotherapy with increased acute leukemia, suggesting that approximately 2% of all the 64,747 cases of second cancer and 7% of the 15,813 excess cases of second cancer in the cohort may be attributable to adjuvant therapies, the study authors estimated.
“This information is of value to patients with early breast cancer and to the clinicians who care for them,” they wrote. Limitations include that the study lacked data on family history, genetic predisposition, and lifestyle choices, including smoking.
An accompanying editorial highlighted the findings on the cancer risks of endocrine and other therapies. “In general, the benefits of treatments in protecting patients from recurrence of breast cancer far outweigh the potential downsides,” they wrote. “Such information should be available and offered by clinicians at the time that adjuvant therapies are discussed.”