ID1 and neoplasm: In our study, among the various bone marrow cell populations, only VEGFR1+ bone marrow cells, which have been defined as hematopoietic progenitor cells that are recruited to distant organs to create a permissive microenvironment that is conducive to cancer metastasis36, 41, were found to be affected by Id1-induced IGF2 and could functionally promote tumour growth and metastasis (Figs 5 and 7).