Population based observational cohort study of second cancers in women diagnosed with early invasive breast cancer in England

Breast cancer survivors are at increased risk of developing second primary cancers, but the methods that have been used to estimate this risk are inconsistent and varying associations have been reported with different cancer types. A population based observational cohort study of 475,000 women with early invasive breast cancer diagnosed in England during 1993-2016 found that the 20-year absolute excess risk of contralateral breast cancer was approximately 3% overall, but larger for younger women and those with lobular phenotype or higher stage disease at index breast cancer diagnosis. The 20-year absolute excess risk of non-breast primary cancer was smaller (approximately 2%), with lung and uterine cancer contributing most of the risk. Adjuvant radiotherapy and systemic therapies were associated with around 7% of the excess number of cancers. The authors conclude that the risk of a second primary cancer in women treated for early invasive breast cancer is slightly higher than for women in the general population.