Primary Cilia in the Breast and Breast Cancer

Primary cilia are non-motile, microtubule-based appendages extending from the surfaces of most vertebrate cells. The function of primary cilia is cell-type dependent. However, they are known to serve as sensors of the extracellular environment by sensing mechanical forces and chemical constituents in several different cell types. They also function as critical platforms for several signaling pathways, including hedgehog and platelet derived growth factor (PDGF) signaling, and function in maintaining cell polarity. While present on many types of normal cells, including epithelial cells of the breast, they have been shown to be decreased or absent in many cancers. This review discusses the relative decrease in primary cilia in a variety of cancers and the known consequences of the presence or absence of primary cilia during tumorigenesis. This review also addresses possible etiologies for the loss of primary cilia in cancer, potential functions for primary cilia in human breast epithelium and subsequent consequences of the loss of primary cilia during breast carcinogenesis.