Disclosed herein are specific 6-heteroaryl substituted pyrido[2,3-d]pyrimidin-7-one compounds as defined in specification, processes for their preparation, compositions comprising said compounds and uses thereof. Said compounds are useful as inhibitors of phosphatidylinositol 3-kinase (PI3K) signalling pathways are therefore useful in the treatment of cancer, in particular breast cancer, colon cancer, rectal cancer, endometrial cancer, gastric carcinoma, glioblastoma, hepatocellular carcinoma, small cell lung cancer, non-small cell lung cancer, melanoma, ovarian cancer, cervical cancer, pancreatic cancer, prostate carcinoma, acute myelogenous leukemia (AML), chronic 15 myelogenous leukemia (CML), non-Hodgkins lymphoma, or thyroid carcinoma.
