Ramón Salazar
Head of Medical Oncology at the Catalan Institute of Oncology (ICO), head of the Colorectal Cancer Research Group, Oncobell programme (IDIBELL) and associate professor of Medicine at the University of Barcelona
Overall, this is a high-quality study: a population cohort in England with 476,373 women with early breast cancer who underwent surgery, follow-up for up to 20 years, and analysis by age and treatment, published in The BMJ. The main finding is reassuring: the long-term risk of a second primary cancer is low—only ~2-3% above that of the general population—with absolute excesses at 20 years of +2.1% for non-breast tumours and +3.1% for contralateral breast cancer (more pronounced in young women).
In addition, the authors and a patient opinion piece they cite point out that many survivors tend to overestimate this risk, so these data help to correct that perception.
It is key to differentiate between second cancer and relapse: the former is a new, independent tumour; relapse is the return of the initial tumour, and this study only evaluates the former.
As for limitations, some registry data may be incomplete, and family history, genetic predisposition, and lifestyle habits (e.g., smoking) are not available, which may affect certain associations. Even so, the sample size allows for accurate estimates and suggests that a small portion of the excess could be related to adjuvant therapies (radiotherapy with contralateral/lung, hormone therapy with endometrium, and chemotherapy with leukaemia), although the benefits of these treatments far outweigh these risks.
In practice, this does not change indications. I believe it may be reassuring for patients with breast cancer currently undergoing treatment and provides a basis for more balanced advice, proportionate follow-up and reinforcement of standard age-based prevention and screening.