Bayer are developing copanlisib (Aliqopa™)-a pan-class I phosphoinositide 3-kinase (PI3K) inhibitor-as a treatment for various haematological and solid malignancies. The US FDA has granted copanlisib accelerated approval for the treatment of adults with relapsed follicular lymphoma who have received at least two prior systemic therapies based on the results of a phase II trial. Phase III trials are underway evaluating copanlisib as treatment for relapsed/refractory diffuse large B-cell lymphoma and in combination with rituximab or rituximab-based chemotherapy or standard immunochemotherapy in patients with relapsed indolent B-cell non-Hodgkin's lymphoma. Phase I/II studies are underway in relapsed or refractory peripheral T-cell or NK/T-cell lymphoma, advanced cholangiocarcinoma, hormone receptor-positive HER2-negative stage I-IV breast cancer, HER2-positive breast cancer and recurrent and/or metastatic head and neck squamous cell carcinomas harbouring a PI3KCA mutation/amplification and/or a PTEN loss. This article summarizes the milestones in the development of copanlisib leading to this first approval for relapsed follicular lymphoma.