The present invention relates to methods of diagnosing and/or prognosing proliferative disorders, especially brain cancers (e.g. gliomas). In particular, the present invention provides a means to conveniently detect malignant tumours merely by assaying or analysing blood (particularly blood serum). Cytokines and/or angiogenesis factors in blood serum have been found to be surprisingly powerful at indicating the presence of brain cancers in a subject. Moreover, spectroscopic analysis, especially ATR-FTIR analysis, of a blood sample has been demonstrated to be surprisingly effective at producing a signature that can be correlated with the presence, extent, severity, or aggressiveness of malignant tumours in a subject.