Although the impairment in the formation of cancer metastases in mice injected with Arl13b-depleted breast cancer cells is consistent with in vitro studies pointing to Arl13b being essential for cancer cell migration and invasion, further studies should be performed where primary tumors are allowed to develop and only then Arl13b is depleted, by using an inducible system. The gene discussed is ARL13B; the disease is breast cancer.