Updated project metadata. Low grade serous ovarian cancer (LGSC) is a rare subtype of ovarian cancer, characterized by a slow growth rate, resistance to current treatment regimens, multiple recurrences and poor survival. LGSC arise from serous borderline tumor (SBT), however the mechanism of transformation is poorly understood. To better understand the biology of serous ovarian tumors, we performed whole proteome profiling of LGSC, SBT and the more common high grade serous (HGSC) ovarian tumors. Proteins associated with the tumor microenvironment were differentially expressed between LGSC and SBT or HGSC. In particular, fibroblast activation protein (FAP), a protein expressed in cancer associated fibroblasts, is abundantly expressed in LGSC. Furthermore, Tregs and M2 macrophages are more abundant in the stroma of LGSC compared to SBT. Together these data suggest that the tumor microenvironment provides a supportive environment for LGSC tumorigenesis and progression, and that targeting the tumor microenvironment of LGSC may be a viable therapeutic strategy.