For instance, in a murine orthotopic model (Box 1) of metastatic breast cancer, circulating tumour cells (CTCs) purified from blood exhibited increased transcription of the coactivator PPARGC1A (peroxisome proliferator-activated receptor gamma, coactivator 1 alpha; also known as PGC-1α) relative to the primary breast tumour or matched lung metastasis. The gene discussed is PPARGC1A; the disease is breast carcinoma.