Abstract Ovarian cancer has the highest mortality among the gynecologic malignancies. The phosphatidylinositol 3-kinase (PI3K) pathway is frequently activated, leading to increased cell survival. This study aimed to identify secreted proteins regulated by the PI3K pathway in ovarian cancer cell lines. Surface-enhanced laser desorption-ionization time-of-flight mass spectrometry with cation-exchange protein-chips was used to analyze secreted proteins from five ovarian cancer cell lines (SKOV-3, PE01, OVCAR-3, OV167, and OV207). To activate the PI3K pathway, cells were treated with 50 ng/mL epidermal growth factor (EGF) with or without 10 μmol/L LY294002, a PI3K inhibitor. Proteins induced by EGF and inhibited by LY294002, in the m/z range 7,500 to 9,500, were purified chromatographically, identified by peptide mass fingerprinting and NH2-terminal sequencing, and confirmed by immunodepletion. Two immunologically related proteins, m/z ∼8,385 and 8,922, were identified as truncated and intact forms, respectively, of interleukin 8, a chemokine previously shown to be elevated in serum of ovarian cancer patients. Another protein, m/z 7,866, was identified as CXC chemokine ligand 1 (CXCL1) or GRO-α, a chemokine associated with melanoma formation and some epithelial cancers. EGF-stimulated CXCL1 levels were variably decreased by mitogen-activated protein kinase (MAPK)/extracellular signal–regulated kinase kinase and p38 MAPK inhibition in the five cell lines, but only LY294002 fully reversed the EGF effect in all cell lines. Immunoreactive CXCL1 levels in 160 conditioned media were highly correlated with corresponding peak intensities at m/z 7,866 by mass spectrometry, indicating the quantitative nature of these analyses. We conclude that proteomic analysis of cell models of human disease may facilitate the discovery of pathway-dependent proteins. (Cancer Res 2006; 66(3): 1376-83)