VHL and neoplasm: Our data suggest that reduced expression of PTHrP in the primary tumor may, in part, mediate the decreased bone dissemination in Hif2α−/− PyMT+ mice, while increased C-X-C chemokine motif receptor 4 (CXCR4) expression may be involved in the regulation of bone dissemination in Vhl−/− PyMT+ mice, although it is important to note that neither gene was significantly changed.