The phosphatidylinositol 3-kinase (PI3K) cell signal transduction pathway plays a central role in critical cell processes, such as proliferation, apoptosis, metabolism, and angiogenesis. But mutations in several of the enzymes in the PI3K pathway have been implicated in the pathogenesis of several types of cancer. As such, the family of enzymes comprising the PI3K pathway presents an opportunity for potential cancer therapies. Targeted development of PI3K pathway inhibitors is a complicated endeavor, but recent cancer genome research has opened new treatment targets and drug-development paradigms with relevance to PI3K. Tumor cell panels offer a platform for evaluating anticancer agents. ATCC has developed several cell panels with tumor cell lines that feature mutations along the PI3K pathway. Also, ATCC has created gene mutation lists that contain annotations of its tumor cell line collection with data from the Sanger Institute COSMIC database. These research tools inform the use of the cell lines as model systems and for drug development. This module discusses the PI3K pathway mutation cell lines and gene mutations lists.