In in vitro experiments, treatment of HB cell lines with the DNA demethylating drug 5-azacytidine restored HHIP protein expression, increased tumor cell apoptosis, and reduced tumor activity, indicating that abnormal activation of the Hh pathway caused by hypermethylation of the HHIP gene plays an important role in the occurrence and development of HB [48] (Fig. 1). Here, HHIP is linked to neoplasm.