p75/AIRM1 is expressed on myeloid cells at stages of differentiation and determination of its presence is useful in monitoring cellular proliferation and determining proliferative states of cells, especially myeloid cells in diseases such as chronic myeloid leukemia. Ligands such as antibody molecules, for instance the QA79 monoclonal antibody deposited under accession number ICLC No. PD99003, are useful for methods of diagnosis and treatment, e.g. by way of inhibition of cellular proliferation and induction of apoptosis in cells.