Second cancers in 475 000 women with early invasive breast cancer diagnosed in England during 1993-2016: population based observational cohort study

McGale P, Dodwell D, Challenger A, Cutter D, Williams A, Broggio J et al. Second cancers in 475 000 women with early invasive breast cancer diagnosed in England during 1993-2016: population based observational cohort study BMJ 2025; 390 :e083975 doi:10.1136/bmj-2024-083975

A large population-based cohort study investigated the long-term risk of developing second primary cancers among women treated for early invasive breast cancer. Using data from the English cancer registries, researchers analysed 476,373 women diagnosed with breast cancer as their first invasive cancer between 1993 and 2016, with follow-up to October 2021.

The study found that women treated for early breast cancer have a slightly higher risk of developing a second primary cancer compared with women in the general population. Approximately 60% of this excess risk was due to contralateral breast cancer, with the greatest increase seen in younger women. Although certain adjuvant treatments were associated with small increases in the risk of specific cancers, the overall contribution of treatment-related cancers was low. Generally, causality can be challenging to prove when analysing observational data, but several associations previously identified from randomised trials were observed, including a reduction in contralateral cancers due to endocrine therapy.

Overall, the findings are reassuring. While breast cancer survivors face a modestly elevated risk of developing a second cancer, the long-term risks associated with modern adjuvant therapies remain small compared with their proven benefits.

These findings, together with ongoing research examining cause-specific mortality following early breast cancer, were presented at the ABS Conference 2026 in Glasgow.

Summary author: Mr Gurdeep Mannu, Cancer Research UK Clinician Scientist, University of Oxford