Taken together, the results of the orthotopic implantation and transwell assays are broadly consistent with our genetic linkage and expression correlation analyses that showed an association of the DBA haplotype on chromosome 13 with metastatic progression in the MMTV-PyMT×AKXD mice, and validate a functional role of Arid4b polymorphism in modulating the breast cancer phenotype. The gene discussed is ARID4B; the disease is breast carcinoma.