PKM and cancer: Furthermore, lactate produced by stromal cells, such as CAFs [83], or aldehyde dehydrogenase 1 family member A3 (ALDH1A3)-induced PKM2 tetramerization [84] activities in addition to sources described above preferentially maintains cancer cell stemness in many cancer types, including triple-negative breast cancer [85], liver cancer [86,87], glioma [88], glioblastoma [84], and colorectal cancer [89].