SHH and central nervous system cancer: In addition, CSCs in human gliomas also require SHH pathway activity for their proliferation, survival and tumorigenicity [107]; (4) Recent studies [120] suggest that there is an association between the expression of the stem cell marker ALDH1 and HER2 amplification in breast tumors, and the clinical efficacy of HER2-targeting agents may correlate with their ability to target breast CSCs.