The invention relates to a novel lipid kinase which is part of the PI3 Kinase family. PI3 Kinases catalyze the addition of phosphate to inositol generating inositol mono, di and triphosphate. Inositol phosphates have been implicated in regulating intracellular signaling cascades resulting in alternations in gene expression which, amongst other effects, can result in cytoskeletal remodeling and modulation of cellular motility. More particularly the invention relates to a novel human PI3 Kinase, p110.DELTA. which interacts with p85, has a broad phosphinositide specificity and is sensitive to the same kinase inhibitors as PI3 Kinase p110A. However, in contrast to previously identified PI3 Kinases which show a ubiquitous pattern of expression, p110.DELTA. is selectively expressed in leucocytes. Importantly, p110.DELTA. shows enhanced expression in most melanomas tested and therefore may play a crucial role in regulating the metastatic property exhibited by melanomas. The identification of agents that enhance or reduce p110.DELTA. activity may therefore prevent cancer metastatis.