PIK3R1 and carcinosarcoma: The PI3-kinase pathway was activated in over half of the carcinosarcomas through alterations in PIK3CA, PIK3R1 and PTEN. Targeted inhibition of this pathway using PI3K/mammalian target of rapamycin/AKT/MEK inhibitors has been reported and is being studied in ongoing Phase I and II trials in endometrial cancer and other tumour types46, 47, 48, 49.