PKM and breast cancer: For example, extracellular PKM2 was reported to stimulate the epidermal growth factor (EGF) receptor and its downstream phosphorylation in breast cancer cell lines, mediated by protein kinase B (Akt) and extracellular signal-regulated kinase (ERK).31 Although the contribution of EGF receptor to axonal growth in neurons is controversial,36 its stimulation was shown to enhance muscle satellite cell activation.37 Therefore, it is necessary to identify the direct target molecules of extracellular PKM2 in neurons and skeletal muscle cells, which might or might not include EGF receptor.