To interrogate the function of PRAK in tumor metastasis, we crossbred the Prak-deficient mouse with the mouse mammary tumor virus-Polyoma virus middle T-antigen (MMTV-PyMT) mouse, which spontaneously develops breast cancer with the occurrence of lung metastases at the age of 12–14 weeks24. The gene discussed is MAPKAPK5; the disease is neoplasm.