text: HER2 is overexpressed in 20-30% of breast cancers and is commonly associated with poor prognosis. It is therefore an oncogene whose differently spliced variants have been shown to have different functions. Knocking down hnRNP H1 was shown to increase the amount of an oncogenic variant Δ16HER2. HER2 is an upstream regulator of cyclin D1 and p27, and its overexpression leads to the deregulation of the G1/S checkpoint.