Population-based cohort study of cumulative incidence of second primary cancers in a large cohort of Danish cancer survivors

A new primary cancer is a serious late effect of a pre-existing cancer diagnosis. A retrospective cohort study in Denmark included 457,334 adults diagnosed with cancer and alive 1 year after diagnosis. The cumulative incidence of second primary cancers increased over time to 6.3% five years after diagnosis to 10.5% ten years after diagnosis and 13.5% fifteen years after diagnosis. The highest cumulative incidence of second primary cancer ten years after diagnosis was observed for cancers of the larynx (21.8%), oropharynx and oral cavity (19.5%), and bladder and urinary tract (18.5%). Survivors of cancers related to alcohol, smoking, diet high in red or processed meat, or virus were at increased risk of developing a second cancer with the same etiology, whereas having had a hormone-related first cancer was associated with lower risk of a second hormone-related cancer.