Peripheral chondrosarcoma (PCS) remains a malignancy for which no treatments other than radical surgery have proven effective. Nonetheless, PCS is one of very few sarcomas which arise from known precursor lesions in the setting of a genetically well-understood heritable syndrome. PCS frequently demonstrates grossly invasive lobular growth patterns and aneuploidy despite generally low-grade histology. One possible explanation is that chondrosarcoma cells have lost their sense of direction. As preliminary data, we found not only misorientation, but a decrease in the presence of primary cilia in the osteochondromas that form in our previously published mouse genetic model of multiple osteochondromas by Ext1 disruption. We now report the first mouse genetic model of peripheral chondrosarcoma, which is completely penetrant. We propose to evaluate polarity in this new mouse model, by staining cilia with antibodies against acetylated microtubules in PCS chondrocytes or osteochondroma control chondrocytes from 9 month old mice in each genotype. We will further analyze DNA ploidy status using a histologically localizable strategy of fluorescent in situ hybridization to identify nuclear copy number of loci that are not focally aberrant in copy number by comparative genomic hybridization. Some genes converge on mechanisms that impact both polarity and ploidy at the level of the microtubule organizing center and the centriole, both of which function in ciliagenesis and mitotic spindle assembly. These pathways will be interrogated regarding the potential impact of Ext1 and tumor suppressor silencing by harvesting mouse chondrocytes and inducing the silencing of the conditional genes in vitro, permiting closely controlled conditions for profiling of expression of ciliagenesis/spindle assembly genes by quantitative PCR. This work is done in collaboration with a team verifying the findings in human specimens for joint publication that we anticipate will identify critical targets for further investigation in both PCS and other cancers.