Similarly, the transcription coactivator peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC-1α), a known mediator of mitochondrial biogenesis, has been shown to be overexpressed in circulating tumor cells (with CSC characteristics) from the MMTV-PyMT spontaneous mouse breast cancer model [43]. The gene discussed is PPARGC1A; the disease is breast cancer.