Abstract: Disclosed are two methods of treating or preventing a proliferative disease as characterized and/or diagnosed by at least one selected from an accumulation of branched-chain amino acid(s) (BCAA), suppression of activity or transcripts level of BCAA catabolic enzyme(s) and a decrease in acylcarnitine level (C5:1), one comprising the administration of a BCAA catabolism enhancer and/or branched chain alpha-ketoacid dehydrogenase complex (BCKDC) kinase inhibitor and the other comprising administration of a meal replacement with low BCAA levels. In three separate embodiments, methods of diagnosis or prognosis are disclosed, each comprising the measurement of the levels of a different marker, i.e. BCAA, BCAA catabolic enzymes or acylcarnitine (C5:1). In preferred embodiments, the proliferative disease is cancer. Also disclosed is a kit or microarray chip useful for methods thereof.