The non-receptor tyrosine kinase (TK) Src is the first oncogene ever identified. In tumors, Src hyperactivation is usually linked to the aberrant activation of upstream receptor tyrosine kinases (RTKs). In previous work, researchers from IRCCS-Fondazione Santa Lucia and collaborators developed a library of pyrazolo[3,4-d]pyrimidines inhibiting Src and other cytoplasmic TKs. Several compounds showed in vitro and in vivo activity in tumor models characterized by a deregulation of those kinases, such as osteosarcoma, neuroblastoma and glioblastoma.