Comparison with conventional markers of tumour mass (eg CA15.3, CEA) and known novel markers of bone metabolism (eg PICP, PINP, ICTP) (both in the diagnosis and in the monitoring of response to systemic therapy), and identification of the pattern of changes of serum FA-2 levels in relation to bisphosphonate therapy and events such as hypercalcaemia are areas that need to be explored before the use of FA-2 could be incorporated into daily clinical practice. The gene discussed is CEACAM5; the disease is neoplasm.