To determine if bone marrow cells primed by the presence of Id1-expressing tumour can directly facilitate tumour growth by interacting with cancer cells, bone marrow was collected 2 weeks after nude mice had been subcutaneously inoculated with KYSE150 cells expressing Id1, Id1-shIGF2 or vector control, and then admixed with parental KYSE150 cells for establishment of subcutaneous tumours in new groups of nude mice (Fig. 7a). The gene discussed is ID1; the disease is cancer.