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

In this study, 475,000 women diagnosed with early invasive breast cancer in England between 1993 and 2016 were followed until October 2021 to assess the risk of a second primary cancer.

By 20 years, 13.6% of the women studied had developed a second primary non-breast cancer, 2.1% more than the general population and 5.6% had developed contralateral breast cancer, 3.1% more than expected in the general population.

For second primary non-breast cancers, the 20-year absolute excess risk was mostly from womb (non-cervix) and lung cancers. For all other cancer types, these excess risks were less than 0.2%.

For women who were diagnosed with contralateral breast, the risk was higher for women who were younger when they were diagnosed, had larger tumours, had a diagnosis in earlier calendar years, had lobular cancer or had oestrogen-receptor negative cancer.

When looking at risks associated with treatments the women had received for their original cancer, around 2% of all second primary cancers and around 7% of the excess number of second cancers were associated with radiotherapy, hormone therapy, or chemotherapy.